1
|
Johnston KE, Almhjell PJ, Watkins-Dulaney EJ, Liu G, Porter NJ, Yang J, Arnold FH. A combinatorially complete epistatic fitness landscape in an enzyme active site. Proc Natl Acad Sci U S A 2024; 121:e2400439121. [PMID: 39074291 PMCID: PMC11317637 DOI: 10.1073/pnas.2400439121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2024] [Accepted: 06/17/2024] [Indexed: 07/31/2024] Open
Abstract
Protein engineering often targets binding pockets or active sites which are enriched in epistasis-nonadditive interactions between amino acid substitutions-and where the combined effects of multiple single substitutions are difficult to predict. Few existing sequence-fitness datasets capture epistasis at large scale, especially for enzyme catalysis, limiting the development and assessment of model-guided enzyme engineering approaches. We present here a combinatorially complete, 160,000-variant fitness landscape across four residues in the active site of an enzyme. Assaying the native reaction of a thermostable β-subunit of tryptophan synthase (TrpB) in a nonnative environment yielded a landscape characterized by significant epistasis and many local optima. These effects prevent simulated directed evolution approaches from efficiently reaching the global optimum. There is nonetheless wide variability in the effectiveness of different directed evolution approaches, which together provide experimental benchmarks for computational and machine learning workflows. The most-fit TrpB variants contain a substitution that is nearly absent in natural TrpB sequences-a result that conservation-based predictions would not capture. Thus, although fitness prediction using evolutionary data can enrich in more-active variants, these approaches struggle to identify and differentiate among the most-active variants, even for this near-native function. Overall, this work presents a large-scale testing ground for model-guided enzyme engineering and suggests that efficient navigation of epistatic fitness landscapes can be improved by advances in both machine learning and physical modeling.
Collapse
Affiliation(s)
- Kadina E. Johnston
- Division of Biology and Bioengineering, California Institute of Technology, Pasadena, CA91125
| | - Patrick J. Almhjell
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA91125
| | - Ella J. Watkins-Dulaney
- Division of Biology and Bioengineering, California Institute of Technology, Pasadena, CA91125
| | - Grace Liu
- Division of Biology and Bioengineering, California Institute of Technology, Pasadena, CA91125
| | - Nicholas J. Porter
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA91125
| | - Jason Yang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA91125
| | - Frances H. Arnold
- Division of Biology and Bioengineering, California Institute of Technology, Pasadena, CA91125
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA91125
| |
Collapse
|
2
|
Bell D, Lindemann F, Gerland L, Aucharova H, Klein A, Friedrich D, Hiller M, Grohe K, Meier T, van Rossum B, Diehl A, Hughes J, Mueller LJ, Linser R, Miller AF, Oschkinat H. Sedimentation of large, soluble proteins up to 140 kDa for 1H-detected MAS NMR and 13C DNP NMR - practical aspects. JOURNAL OF BIOMOLECULAR NMR 2024:10.1007/s10858-024-00444-9. [PMID: 38904893 DOI: 10.1007/s10858-024-00444-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2024] [Accepted: 05/08/2024] [Indexed: 06/22/2024]
Abstract
Solution NMR is typically applied to biological systems with molecular weights < 40 kDa whereas magic-angle-spinning (MAS) solid-state NMR traditionally targets very large, oligomeric proteins and complexes exceeding 500 kDa in mass, including fibrils and crystalline protein preparations. Here, we propose that the gap between these size regimes can be filled by the approach presented that enables investigation of large, soluble and fully protonated proteins in the range of 40-140 kDa. As a key step, ultracentrifugation produces a highly concentrated, gel-like state, resembling a dense phase in spontaneous liquid-liquid phase separation (LLPS). By means of three examples, a Sulfolobus acidocaldarius bifurcating electron transfer flavoprotein (SaETF), tryptophan synthases from Salmonella typhimurium (StTS) and their dimeric β-subunits from Pyrococcus furiosus (PfTrpB), we show that such samples yield well-resolved proton-detected 2D and 3D NMR spectra at 100 kHz MAS without heterogeneous broadening, similar to diluted liquids. Herein, we provide practical guidance on centrifugation conditions and tools, sample behavior, and line widths expected. We demonstrate that the observed chemical shifts correspond to those obtained from µM/low mM solutions or crystalline samples, indicating structural integrity. Nitrogen line widths as low as 20-30 Hz are observed. The presented approach is advantageous for proteins or nucleic acids that cannot be deuterated due to the expression system used, or where relevant protons cannot be re-incorporated after expression in deuterated medium, and it circumvents crystallization. Importantly, it allows the use of low-glycerol buffers in dynamic nuclear polarization (DNP) NMR of proteins as demonstrated with the cyanobacterial phytochrome Cph1.
Collapse
Affiliation(s)
- Dallas Bell
- Faculty II-Mathematics and Natural Sciences, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Florian Lindemann
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Lisa Gerland
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Hanna Aucharova
- Department of Chemistry and Chemical Biology, TU Dortmund University, Otto-Hahn-Str. 4a, 44227, Dortmund, Germany
| | - Alexander Klein
- Department of Chemistry and Chemical Biology, TU Dortmund University, Otto-Hahn-Str. 4a, 44227, Dortmund, Germany
| | - Daniel Friedrich
- Department of Chemistry and Biochemistry, University of Cologne, Greinstr. 4, 50939, Cologne, Germany
| | - Matthias Hiller
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Kristof Grohe
- Bruker BioSpin GmbH & Co. KG, Rudolf-Plank-Str. 23, 76275, Ettlingen, Germany
| | - Tobias Meier
- Bruker BioSpin GmbH & Co. KG, Rudolf-Plank-Str. 23, 76275, Ettlingen, Germany
| | - Barth van Rossum
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Anne Diehl
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Jon Hughes
- Institute for Plant Physiology, Justus Liebig University, Senckenbergstr. 3, 35360, Gießen, Germany
- Department of Physics, Free University of Berlin, Arnimallee 14, 14195, Berlin, Germany
| | - Leonard J Mueller
- Department of Chemistry, University of California - Riverside, Riverside, CA, 92521, USA
| | - Rasmus Linser
- Department of Chemistry and Chemical Biology, TU Dortmund University, Otto-Hahn-Str. 4a, 44227, Dortmund, Germany
| | - Anne-Frances Miller
- Faculty II-Mathematics and Natural Sciences, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany.
- Department of Chemistry, University of Kentucky, Lexington, KY, 40506, USA.
| | - Hartmut Oschkinat
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany.
| |
Collapse
|
3
|
Bell D, Lindemann F, Gerland L, Aucharova H, Klein A, Friedrich D, Hiller M, Grohe K, van Rossum B, Diehl A, Hughes J, Mueller LJ, Linser R, Miller AF, Oschkinat H. Sedimentation of large, soluble proteins up to 140 kDa for 1H-detected MAS NMR and 13C DNP NMR - practical aspects. RESEARCH SQUARE 2024:rs.3.rs-3972885. [PMID: 38464080 PMCID: PMC10925473 DOI: 10.21203/rs.3.rs-3972885/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/12/2024]
Abstract
Solution NMR is typically applied to biological systems with molecular weights < 40 kDa whereas magic-angle-spinning (MAS) solid-state NMR traditionally targets very large, oligomeric proteins and complexes exceeding 500 kDa in mass, including fibrils and crystalline protein preparations. Here, we propose that the gap between these size regimes can be filled by the approach presented that enables investigation of large, soluble and fully protonated proteins in the range of 40-140 kDa. As a key step, ultracentrifugation produces a highly concentrated, gel-like state, resembling a dense phase in spontaneous liquid-liquid phase separation (LLPS). By means of three examples, a Sulfolobus acidocaldarius bifurcating electron transfer flavoprotein (SulfETF), tryptophan synthases from Salmonella typhimurium (StTS) and the dimeric β-subunits from Pyrococcus furiosus (PfTrpB), we show that such samples yield well-resolved proton-detected 2D and 3D NMR spectra at 100 kHz MAS without heterogeneous broadening, similar to diluted liquids. Herein, we provide practical guidance on centrifugation conditions and tools, sample behavior, and line widths expected. We demonstrate that the observed chemical shifts correspond to those obtained from μM/low mM solutions or crystalline samples, indicating structural integrity. Nitrogen line widths as low as 20-30 Hz are observed. The presented approach is advantageous for proteins or nucleic acids that cannot be deuterated due to the expression system used, or where relevant protons cannot be re-incorporated after expression in deuterated medium, and it circumvents crystallization. Importantly, it allows the use of low-glycerol buffers in dynamic nuclear polarization (DNP) NMR of proteins as demonstrated with the cyanobacterial phytochrome Cph1.
Collapse
Affiliation(s)
- Dallas Bell
- Faculty II-Mathematics and Natural Sciences, Technische Universität Berlin
| | | | - Lisa Gerland
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie
| | - Hanna Aucharova
- Department of Chemistry and Chemical Biology, TU Dortmund University
| | - Alexander Klein
- Department of Chemistry and Chemical Biology, TU Dortmund University
| | | | | | | | | | - Anne Diehl
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie
| | - Jon Hughes
- Justus Liebig University, Institute for Plant Physiology
| | | | - Rasmus Linser
- Department of Chemistry and Chemical Biology, TU Dortmund University
| | | | | |
Collapse
|
4
|
Martins NF, Viana MJA, Maigret B. Fungi Tryptophan Synthases: What Is the Role of the Linker Connecting the α and β Structural Domains in Hemileia vastatrix TRPS? A Molecular Dynamics Investigation. Molecules 2024; 29:756. [PMID: 38398508 PMCID: PMC10893352 DOI: 10.3390/molecules29040756] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2023] [Revised: 01/25/2024] [Accepted: 01/30/2024] [Indexed: 02/25/2024] Open
Abstract
Tryptophan synthase (TRPS) is a complex enzyme responsible for tryptophan biosynthesis. It occurs in bacteria, plants, and fungi as an αββα heterotetramer. Although encoded by independent genes in bacteria and plants, in fungi, TRPS is generated by a single gene that concurrently expresses the α and β entities, which are linked by an elongated peculiar segment. We conducted 1 µs all-atom molecular dynamics simulations on Hemileia vastatrix TRPS to address two questions: (i) the role of the linker segment and (ii) the comparative mode of action. Since there is not an experimental structure, we started our simulations with homology modeling. Based on the results, it seems that TRPS makes use of an already-existing tunnel that can spontaneously move the indole moiety from the α catalytic pocket to the β one. Such behavior was completely disrupted in the simulation without the linker. In light of these results and the αβ dimer's low stability, the full-working TRPS single genes might be the result of a particular evolution. Considering the significant losses that Hemileia vastatrix causes to coffee plantations, our next course of action will be to use the TRPS to look for substances that can block tryptophan production and therefore control the disease.
Collapse
Affiliation(s)
- Natália F Martins
- EMBRAPA Agroindústria Tropical, Planalto do Pici, Fortaleza 60511-110, CE, Brazil
| | - Marcos J A Viana
- EMBRAPA Agroindústria Tropical, Planalto do Pici, Fortaleza 60511-110, CE, Brazil
| | - Bernard Maigret
- LORIA, UMR 7504 CNRS, Université de Lorraine, 54000 Vandoeuvre les Nancy, France
| |
Collapse
|
5
|
Abhishek S, Deeksha W, Nethravathi KR, Davari MD, Rajakumara E. Allosteric crosstalk in modular proteins: Function fine-tuning and drug design. Comput Struct Biotechnol J 2023; 21:5003-5015. [PMID: 37867971 PMCID: PMC10589753 DOI: 10.1016/j.csbj.2023.10.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Revised: 10/07/2023] [Accepted: 10/08/2023] [Indexed: 10/24/2023] Open
Abstract
Modular proteins are regulatory proteins that carry out more than one function. These proteins upregulate or downregulate a biochemical cascade to establish homeostasis in cells. To switch the function or alter the efficiency (based on cellular needs), these proteins require different facilitators that bind to a site different from the catalytic (active/orthosteric) site, aka 'allosteric site', and fine-tune their function. These facilitators (or effectors) are allosteric modulators. In this Review, we have discussed the allostery, characterized them based on their mechanisms, and discussed how allostery plays an important role in the activity modulation and function fine-tuning of proteins. Recently there is an emergence in the discovery of allosteric drugs. We have also emphasized the role, significance, and future of allostery in therapeutic applications.
Collapse
Affiliation(s)
- Suman Abhishek
- Macromolecular Structural Biology lab, Department of Biotechnology, Indian Institute of Technology Hyderabad, Telangana 502284, India
| | - Waghela Deeksha
- Macromolecular Structural Biology lab, Department of Biotechnology, Indian Institute of Technology Hyderabad, Telangana 502284, India
| | | | - Mehdi D. Davari
- Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Halle 06120, Germany
| | - Eerappa Rajakumara
- Macromolecular Structural Biology lab, Department of Biotechnology, Indian Institute of Technology Hyderabad, Telangana 502284, India
| |
Collapse
|
6
|
Phillips RS, Bauer O. Characterization of aminoacrylate intermediates of pyridoxal-5'-phosphate dependent enzymes. Methods Enzymol 2023; 685:199-224. [PMID: 37245902 DOI: 10.1016/bs.mie.2023.03.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Pyridoxal-5'-phosphate (PLP) Schiff's bases of 2-aminoacrylate are intermediates in β-elimination and β-substitution reaction of PLP-dependent enzymes. These enzymes are found in two major families, the α-, or aminotransferase, superfamily, and the β-family. While the α-family enzymes primarily catalyze β-eliminations, the β-family enzymes catalyze both β-elimination and β-substitution reactions. Tyrosine phenol-lyase (TPL), which catalyzes the reversible elimination of phenol from l-tyrosine, is an example of an α-family enzyme. Tryptophan synthase catalyzes the irreversible formation of l-tryptophan from l-serine and indole, and is an example of a β-family enzyme. The identification and characterization of aminoacrylate intermediates in the reactions of both of these enzymes is discussed. The use of UV-visible absorption and fluorescence spectroscopy, X-ray and neutron crystallography, and NMR spectroscopy to identify aminoacrylate intermediates in these and other PLP enzymes is presented.
Collapse
Affiliation(s)
- Robert S Phillips
- Department of Chemistry, University of Georgia, Athens, GA, United States; Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, United States.
| | - Olivia Bauer
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, United States
| |
Collapse
|
7
|
Chen W, He H, Wang J, Wang J, Chang CEA. Uncovering water effects in protein-ligand recognition: importance in the second hydration shell and binding kinetics. Phys Chem Chem Phys 2023; 25:2098-2109. [PMID: 36562309 PMCID: PMC9970846 DOI: 10.1039/d2cp04584b] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Developing a ligand with high affinity for a specific protein target is essential for drug design, and water molecules are well known to play a key role in protein-drug recognition. However, predicting the role of particularly ordered water molecules in drug binding remains challenging. Furthermore, hydration free energy contributed from the water network, including the second shell of water molecules, is far from being well studied. In this research we focused on these aspects to accurately and efficiently evaluate water effects in protein-ligand binding affinity. We developed a new strategy using a free-energy calculation method, VM2. We successfully predicted the stable ordered water molecules in a number of protein systems: PDE 10a, HSP90, tryptophan synthase (TRPS), CDK2 and Factor Xa. In some of these, the second shell of water molecules appeared to be critical in protein-ligand binding. We also applied the strategy to largely improve binding free energy calculation using the MM/PBSA method. When applying MM/PBSA alone for two systems, CDK2 and Factor Xa, the computed binding free energy resulted in poor to moderate R2 values with experimental data. However, including water free energy correction greatly improved the free energy calculation. Furthermore, our work helped to explain how xk263 is a 1000 times faster binder to HIVp than ritonavir, a potentially useful tool for investigating binding kinetics. Our studies reveal the importance of fully considering water effects in therapeutic developments in pharmaceutical and biotechnology industries and for fundamental research in protein-ligand recognition.
Collapse
Affiliation(s)
- Wei Chen
- School of Pharmacy, Fuzhou Medical College of NanChang University, Fuzhou, JiangXi 344000, P. R. China.
| | - Huan He
- School of Pharmacy, Fuzhou Medical College of NanChang University, Fuzhou, JiangXi 344000, P. R. China.
| | - Jing Wang
- School of Pharmacy, Fuzhou Medical College of NanChang University, Fuzhou, JiangXi 344000, P. R. China.
| | - Jiahui Wang
- School of Pharmacy, Fuzhou Medical College of NanChang University, Fuzhou, JiangXi 344000, P. R. China.
| | - Chia-en A. Chang
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA,Corresponding Authors Wei Chen: School of Pharmacy, Fuzhou Medical College of NanChang University, Fuzhou, JiangXi 344000, China. , Chia-en A. Chang: Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA.
| |
Collapse
|
8
|
Ghosh RK, Hilario E, Chang CEA, Mueller LJ, Dunn MF. Allosteric regulation of substrate channeling: Salmonella typhimurium tryptophan synthase. Front Mol Biosci 2022; 9:923042. [PMID: 36172042 PMCID: PMC9512447 DOI: 10.3389/fmolb.2022.923042] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 08/11/2022] [Indexed: 11/13/2022] Open
Abstract
The regulation of the synthesis of L-tryptophan (L-Trp) in enteric bacteria begins at the level of gene expression where the cellular concentration of L-Trp tightly controls expression of the five enzymes of the Trp operon responsible for the synthesis of L-Trp. Two of these enzymes, trpA and trpB, form an αββα bienzyme complex, designated as tryptophan synthase (TS). TS carries out the last two enzymatic processes comprising the synthesis of L-Trp. The TS α-subunits catalyze the cleavage of 3-indole D-glyceraldehyde 3′-phosphate to indole and D-glyceraldehyde 3-phosphate; the pyridoxal phosphate-requiring β-subunits catalyze a nine-step reaction sequence to replace the L-Ser hydroxyl by indole giving L-Trp and a water molecule. Within αβ dimeric units of the αββα bienzyme complex, the common intermediate indole is channeled from the α site to the β site via an interconnecting 25 Å-long tunnel. The TS system provides an unusual example of allosteric control wherein the structures of the nine different covalent intermediates along the β-reaction catalytic path and substrate binding to the α-site provide the allosteric triggers for switching the αββα system between the open (T) and closed (R) allosteric states. This triggering provides a linkage that couples the allosteric conformational coordinate to the covalent chemical reaction coordinates at the α- and β-sites. This coupling drives the α- and β-sites between T and R conformations to achieve regulation of substrate binding and/or product release, modulation of the α- and β-site catalytic activities, prevention of indole escape from the confines of the active sites and the interconnecting tunnel, and synchronization of the α- and β-site catalytic activities. Here we review recent advances in the understanding of the relationships between structure, function, and allosteric regulation of the complex found in Salmonella typhimurium.
Collapse
Affiliation(s)
- Rittik K. Ghosh
- Department of Biochemistry, University of California, Riverside, Riverside, CA, United States
| | - Eduardo Hilario
- Department of Chemistry, University of California, Riverside, Riverside, CA, United States
| | - Chia-en A. Chang
- Department of Chemistry, University of California, Riverside, Riverside, CA, United States
| | - Leonard J. Mueller
- Department of Chemistry, University of California, Riverside, Riverside, CA, United States
- *Correspondence: Leonard J. Mueller, ; Michael F. Dunn,
| | - Michael F. Dunn
- Department of Biochemistry, University of California, Riverside, Riverside, CA, United States
- *Correspondence: Leonard J. Mueller, ; Michael F. Dunn,
| |
Collapse
|
9
|
l-Serine Biosensor-Controlled Fermentative Production of l-Tryptophan Derivatives by Corynebacterium glutamicum. BIOLOGY 2022; 11:biology11050744. [PMID: 35625472 PMCID: PMC9138238 DOI: 10.3390/biology11050744] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 05/05/2022] [Accepted: 05/10/2022] [Indexed: 11/17/2022]
Abstract
Simple Summary l-tryptophan is an amino acid found in proteins. Its derivatives, such as hydroxylated or halogenated l-tryptophans, find applications in the chemical and pharmaceutical industries, for example, in therapeutic peptides. Biotechnology provides a sustainable way for the production of l-tryptophan and its derivatives. In the final reaction of l-tryptophan biosynthesis in bacteria, such as Corynebacterium glutamicum, another amino acid, l-serine, is incorporated. Here, we show that C. glutamicum TrpB is able to convert indole derivatives, which were added to cells synthesizing l-serine, to the corresponding l-tryptophan derivatives. The gene trpB was expressed under the control of the l-serine-responsive transcriptional activator SerR in the C. glutamicum cells engineered for this fermentation process. Abstract l-Tryptophan derivatives, such as hydroxylated or halogenated l-tryptophans, are used in therapeutic peptides and agrochemicals and as precursors of bioactive compounds, such as serotonin. l-Tryptophan biosynthesis depends on another proteinogenic amino acid, l-serine, which is condensed with indole-3-glycerophosphate by tryptophan synthase. This enzyme is composed of the α-subunit TrpA, which catalyzes the retro-aldol cleavage of indole-3-glycerol phosphate, yielding glyceraldehyde-3-phosphate and indole, and the β-subunit TrpB that catalyzes the β-substitution reaction between indole and l-serine to water and l-tryptophan. TrpA is reported as an allosteric actuator, and its absence severely attenuates TrpB activity. In this study, however, we showed that Corynebacterium glutamicum TrpB is catalytically active in the absence of TrpA. Overexpression of C. glutamicumtrpB in a trpBA double deletion mutant supported growth in minimal medium only when exogenously added indole was taken up into the cell and condensed with intracellularly synthesized l-serine. The fluorescence reporter gene of an l-serine biosensor, which was based on the endogenous transcriptional activator SerR and its target promoter PserE, was replaced by trpB. This allowed for l-serine-dependent expression of trpB in an l-serine-producing strain lacking TrpA. Upon feeding of the respective indole derivatives, this strain produced the l-tryptophan derivatives 5-hydroxytryptophan, 7-bromotryptophan, and 5-fluorotryptophan.
Collapse
|
10
|
Kurisaki I, Tanaka S. Computational prediction of heteromeric protein complex disassembly order using hybrid Monte Carlo/molecular dynamics simulation. Phys Chem Chem Phys 2022; 24:10575-10587. [PMID: 35445673 DOI: 10.1039/d2cp00267a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The physicochemical entities comprising the biological phenomena in the cell form a network of biochemical reactions and the activity of such a network is regulated by multimeric protein complexes. Mass spectroscopy (MS) experiments and multimeric protein docking simulations based on structural bioinformatics techniques have revealed the molecular-level stoichiometry and static configuration of subcomplexes in their bound forms, thus revealing the subcomplex population and formation orders. Meanwhile, these methodologies are not designed to straightforwardly examine the temporal dynamics of multimeric protein assembly and disassembly, essential physicochemical properties to understand the functional expression mechanisms of proteins in the biological environment. To address this problem, we have developed an atomistic simulation in the framework of the hybrid Monte Carlo/molecular dynamics (hMC/MD) method and succeeded in observing the disassembly of a homomeric pentamer of the serum amyloid P component protein in an experimentally consistent order. In this study, we improved the hMC/MD method to examine the disassembly processes of the tryptophan synthase tetramer, a paradigmatic heteromeric protein complex in MS studies. We employed the likelihood-based selection scheme to determine a dissociation-prone subunit pair at every hMC/MD simulation cycle and achieved highly reliable predictions of the disassembly orders without a priori knowledge of the MS experiments and structural bioinformatics simulations. The success rate for the experimentally-observed disassembly order is over 0.9. We similarly succeeded in reliable predictions for three other tetrameric protein complexes. These achievements indicate the potential applicability of our hMC/MD approach as a general-purpose methodology to obtain microscopic and physicochemical insights into multimeric protein complex formation.
Collapse
Affiliation(s)
- Ikuo Kurisaki
- Department of Computational Science, Graduate School of System Informatics, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
| | - Shigenori Tanaka
- Department of Computational Science, Graduate School of System Informatics, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
| |
Collapse
|
11
|
Bosken YK, Ai R, Hilario E, Ghosh RK, Dunn MF, Kan S, Niks D, Zhou H, Ma W, Mueller LJ, Fan L, Chang CA. Discovery of antimicrobial agent targeting tryptophan synthase. Protein Sci 2022; 31:432-442. [PMID: 34767267 PMCID: PMC8820114 DOI: 10.1002/pro.4236] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 10/27/2021] [Accepted: 11/09/2021] [Indexed: 02/03/2023]
Abstract
Antibiotic resistance is a continually growing challenge in the treatment of various bacterial infections worldwide. New drugs and new drug targets are necessary to curb the threat of infectious diseases caused by multidrug-resistant pathogens. The tryptophan biosynthesis pathway is essential for bacterial growth but is absent in higher animals and humans. Drugs that can inhibit the bacterial biosynthesis of tryptophan offer a new class of antibiotics. In this work, we combined a structure-based strategy using in silico docking screening and molecular dynamics (MD) simulations to identify compounds targeting the α subunit of tryptophan synthase with experimental methods involving the whole-cell minimum inhibitory concentration (MIC) test, solution state NMR, and crystallography to confirm the inhibition of L-tryptophan biosynthesis. Screening 1,800 compounds from the National Cancer Institute Diversity Set I against α subunit revealed 28 compounds for experimental validation; four of the 28 hit compounds showed promising activity in MIC testing. We performed solution state NMR experiments to demonstrate that a one successful inhibitor, 3-amino-3-imino-2-phenyldiazenylpropanamide (Compound 1) binds to the α subunit. We also report a crystal structure of Salmonella enterica serotype Typhimurium tryptophan synthase in complex with Compound 1 which revealed a binding site at the αβ interface of the dimeric enzyme. MD simulations were carried out to examine two binding sites for the compound. Our results show that this small molecule inhibitor could be a promising lead for future drug development.
Collapse
Affiliation(s)
- Yuliana K. Bosken
- Department of ChemistryUniversity of California at RiversideRiversideCalifornia
| | - Rizi Ai
- Department of ChemistryUniversity of California at RiversideRiversideCalifornia
| | - Eduardo Hilario
- Department of ChemistryUniversity of California at RiversideRiversideCalifornia
| | - Rittik K. Ghosh
- Department of BiochemistryUniversity of California at RiversideRiversideCalifornia
| | - Michael F. Dunn
- Department of BiochemistryUniversity of California at RiversideRiversideCalifornia
| | - Shih‐Hsin Kan
- Department of ChemistryUniversity of California at RiversideRiversideCalifornia,Present address:
CHOC Research InstituteOrangeCalifornia
| | - Dimitri Niks
- Department of BiochemistryUniversity of California at RiversideRiversideCalifornia
| | - Huanbin Zhou
- Department of Microbiology and Plant PathologyUniversity of California at RiversideRiversideCalifornia,Present address:
Institute of Plant ProtectionChinese Academy of Agricultural SciencesBeijingChina
| | - Wenbo Ma
- Department of Microbiology and Plant PathologyUniversity of California at RiversideRiversideCalifornia,Present address:
The Sainsbury LaboratoryNorwich Research ParkNorwichUK
| | - Leonard J. Mueller
- Department of ChemistryUniversity of California at RiversideRiversideCalifornia
| | - Li Fan
- Department of BiochemistryUniversity of California at RiversideRiversideCalifornia
| | - Chia‐En A. Chang
- Department of ChemistryUniversity of California at RiversideRiversideCalifornia
| |
Collapse
|
12
|
Klein A, Rovó P, Sakhrani VV, Wang Y, Holmes JB, Liu V, Skowronek P, Kukuk L, Vasa SK, Güntert P, Mueller LJ, Linser R. Atomic-resolution chemical characterization of (2x)72-kDa tryptophan synthase via four- and five-dimensional 1H-detected solid-state NMR. Proc Natl Acad Sci U S A 2022; 119:e2114690119. [PMID: 35058365 PMCID: PMC8795498 DOI: 10.1073/pnas.2114690119] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Accepted: 12/13/2021] [Indexed: 02/07/2023] Open
Abstract
NMR chemical shifts provide detailed information on the chemical properties of molecules, thereby complementing structural data from techniques like X-ray crystallography and electron microscopy. Detailed analysis of protein NMR data, however, often hinges on comprehensive, site-specific assignment of backbone resonances, which becomes a bottleneck for molecular weights beyond 40 to 45 kDa. Here, we show that assignments for the (2x)72-kDa protein tryptophan synthase (665 amino acids per asymmetric unit) can be achieved via higher-dimensional, proton-detected, solid-state NMR using a single, 1-mg, uniformly labeled, microcrystalline sample. This framework grants access to atom-specific characterization of chemical properties and relaxation for the backbone and side chains, including those residues important for the catalytic turnover. Combined with first-principles calculations, the chemical shifts in the β-subunit active site suggest a connection between active-site chemistry, the electrostatic environment, and catalytically important dynamics of the portal to the β-subunit from solution.
Collapse
Affiliation(s)
- Alexander Klein
- Department of Chemistry and Pharmacy, Ludwig Maximilians University, 81377 Munich, Germany
- Department of Chemistry and Chemical Biology, TU Dortmund University, 44227 Dortmund, Germany
| | - Petra Rovó
- Department of Chemistry and Pharmacy, Ludwig Maximilians University, 81377 Munich, Germany
| | - Varun V Sakhrani
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Yangyang Wang
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Jacob B Holmes
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Viktoriia Liu
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Patricia Skowronek
- Department of Chemistry and Pharmacy, Ludwig Maximilians University, 81377 Munich, Germany
| | - Laura Kukuk
- Department of Chemistry and Chemical Biology, TU Dortmund University, 44227 Dortmund, Germany
| | - Suresh K Vasa
- Department of Chemistry and Pharmacy, Ludwig Maximilians University, 81377 Munich, Germany
- Department of Chemistry and Chemical Biology, TU Dortmund University, 44227 Dortmund, Germany
| | - Peter Güntert
- Institute of Biophysical Chemistry, Goethe University, 60438 Frankfurt am Main, Germany
- Laboratory of Physical Chemistry, Eidgenössische Technische Hochschule (ETH) Zürich, 8093 Zürich, Switzerland
- Department of Chemistry, Tokyo Metropolitan University, Tokyo 192-0397, Japan
| | - Leonard J Mueller
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Rasmus Linser
- Department of Chemistry and Pharmacy, Ludwig Maximilians University, 81377 Munich, Germany;
- Department of Chemistry and Chemical Biology, TU Dortmund University, 44227 Dortmund, Germany
| |
Collapse
|
13
|
Holmes JB, Liu V, Caulkins BG, Hilario E, Ghosh RK, Drago VN, Young RP, Romero JA, Gill AD, Bogie PM, Paulino J, Wang X, Riviere G, Bosken YK, Struppe J, Hassan A, Guidoulianov J, Perrone B, Mentink-Vigier F, Chang CEA, Long JR, Hooley RJ, Mueser TC, Dunn MF, Mueller LJ. Imaging active site chemistry and protonation states: NMR crystallography of the tryptophan synthase α-aminoacrylate intermediate. Proc Natl Acad Sci U S A 2022; 119:e2109235119. [PMID: 34996869 PMCID: PMC8764694 DOI: 10.1073/pnas.2109235119] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/15/2021] [Indexed: 02/07/2023] Open
Abstract
NMR-assisted crystallography-the integrated application of solid-state NMR, X-ray crystallography, and first-principles computational chemistry-holds significant promise for mechanistic enzymology: by providing atomic-resolution characterization of stable intermediates in enzyme active sites, including hydrogen atom locations and tautomeric equilibria, NMR crystallography offers insight into both structure and chemical dynamics. Here, this integrated approach is used to characterize the tryptophan synthase α-aminoacrylate intermediate, a defining species for pyridoxal-5'-phosphate-dependent enzymes that catalyze β-elimination and replacement reactions. For this intermediate, NMR-assisted crystallography is able to identify the protonation states of the ionizable sites on the cofactor, substrate, and catalytic side chains as well as the location and orientation of crystallographic waters within the active site. Most notable is the water molecule immediately adjacent to the substrate β-carbon, which serves as a hydrogen bond donor to the ε-amino group of the acid-base catalytic residue βLys87. From this analysis, a detailed three-dimensional picture of structure and reactivity emerges, highlighting the fate of the L-serine hydroxyl leaving group and the reaction pathway back to the preceding transition state. Reaction of the α-aminoacrylate intermediate with benzimidazole, an isostere of the natural substrate indole, shows benzimidazole bound in the active site and poised for, but unable to initiate, the subsequent bond formation step. When modeled into the benzimidazole position, indole is positioned with C3 in contact with the α-aminoacrylate Cβ and aligned for nucleophilic attack. Here, the chemically detailed, three-dimensional structure from NMR-assisted crystallography is key to understanding why benzimidazole does not react, while indole does.
Collapse
Affiliation(s)
- Jacob B Holmes
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Viktoriia Liu
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Bethany G Caulkins
- Department of Chemistry, University of California, Riverside, CA 92521
- W.M. Keck Science Department, Claremont McKenna, Pitzer, and Scripps Colleges, Claremont, CA 91711
| | - Eduardo Hilario
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Rittik K Ghosh
- Department of Biochemistry, University of California, Riverside, CA 92521
| | - Victoria N Drago
- Department of Chemistry and Biochemistry, University of Toledo, Toledo, OH 43606
| | - Robert P Young
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354
| | - Jennifer A Romero
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Adam D Gill
- Department of Biochemistry, University of California, Riverside, CA 92521
| | - Paul M Bogie
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Joana Paulino
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310
| | - Xiaoling Wang
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310
| | - Gwladys Riviere
- Department of Biochemistry and Molecular Biology, McKnight Brain Institute, National High Magnetic Field Laboratory, University of Florida, Gainesville, FL 32610
| | - Yuliana K Bosken
- Department of Biochemistry, University of California, Riverside, CA 92521
| | | | - Alia Hassan
- Bruker Switzerland AG 8117 Fällanden, Switzerland
| | | | | | | | - Chia-En A Chang
- Department of Chemistry, University of California, Riverside, CA 92521
| | - Joanna R Long
- Department of Biochemistry and Molecular Biology, McKnight Brain Institute, National High Magnetic Field Laboratory, University of Florida, Gainesville, FL 32610
| | - Richard J Hooley
- Department of Chemistry, University of California, Riverside, CA 92521
- Department of Biochemistry, University of California, Riverside, CA 92521
| | - Timothy C Mueser
- Department of Chemistry and Biochemistry, University of Toledo, Toledo, OH 43606
| | - Michael F Dunn
- Department of Biochemistry, University of California, Riverside, CA 92521;
| | - Leonard J Mueller
- Department of Chemistry, University of California, Riverside, CA 92521;
| |
Collapse
|
14
|
Han J, Lyutenko NV, Sorochinsky AE, Okawara A, Konno H, White S, Soloshonok VA. Tailor-Made Amino Acids in Pharmaceutical Industry: Synthetic Approaches to Aza-Tryptophan Derivatives. Chemistry 2021; 27:17510-17528. [PMID: 34913215 DOI: 10.1002/chem.202102485] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Accepted: 08/24/2021] [Indexed: 12/22/2022]
Abstract
Over the recent years there has been a noticeable upsurge of interest in aza-analogs of tryptophan which are isosteric to the latter and found numerous applications in medicinal, bioorganic chemistry, and peptide research. In the present review article, five aza-tryptophan derivatives are profiled, including aza-substitution in the positions 2, on the five-membered ring, as well as in positions 4, 5, 6, and 7 on the six-membered ring. A detailed and comprehensive literature overview of the synthetic methods for the preparation of these aza-tryptophans is presented and general facets of the biological properties and most promising applications are discussed.
Collapse
Affiliation(s)
- Jianlin Han
- Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources International Innovation Center for Forest Chemicals and Materials College of Chemical Engineering, Nanjing Forestry University, Nanjing, 210037, P. R. China
| | - Nataliya V Lyutenko
- Department of Fine Organic Synthesis V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry, The National Academy of Sciences of Ukraine, 1 Murmanska str., Kyiv, 02094, Ukraine
| | - Alexander E Sorochinsky
- Department of Fine Organic Synthesis V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry, The National Academy of Sciences of Ukraine, 1 Murmanska str., Kyiv, 02094, Ukraine
| | - Ayaka Okawara
- Graduate School of Science and Engineering, Yamagata University, 4-3-16, Jonan, Yonezawa, Yamagata, 992-8510, Japan
| | - Hiroyuki Konno
- Graduate School of Science and Engineering, Yamagata University, 4-3-16, Jonan, Yonezawa, Yamagata, 992-8510, Japan
| | - Sarah White
- Oakwood Chemical, Inc., 730 Columbia Hwy. N, Estill, SC, 29918, USA
| | - Vadim A Soloshonok
- Department of Organic Chemistry I Faculty of Chemistry, University of the Basque Country UPV/EHU, Paseo Manuel Lardizábal 3, 20018, San Sebastián, Spain.,IKERBASQUE, Basque Foundation for Science, María Díaz de Haro 3, Plaza Bizkaia, 48013, Bilbao, Spain
| |
Collapse
|
15
|
Maria-Solano MA, Kinateder T, Iglesias-Fernández J, Sterner R, Osuna S. In Silico Identification and Experimental Validation of Distal Activity-Enhancing Mutations in Tryptophan Synthase. ACS Catal 2021; 11:13733-13743. [PMID: 34777912 PMCID: PMC8576815 DOI: 10.1021/acscatal.1c03950] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 10/12/2021] [Indexed: 12/26/2022]
Abstract
Allostery is a central mechanism for the regulation of multi-enzyme complexes. The mechanistic basis that drives allosteric regulation is poorly understood but harbors key information for enzyme engineering. In the present study, we focus on the tryptophan synthase complex that is composed of TrpA and TrpB subunits, which allosterically activate each other. Specifically, we develop a rational approach for identifying key amino acid residues of TrpB distal from the active site. Those residues are predicted to be crucial for shifting the inefficient conformational ensemble of the isolated TrpB to a productive ensemble through intra-subunit allosteric effects. The experimental validation of the conformationally driven TrpB design demonstrates its superior stand-alone activity in the absence of TrpA, comparable to those enhancements obtained after multiple rounds of experimental laboratory evolution. Our work evidences that the current challenge of distal active site prediction for enhanced function in computational enzyme design has become within reach.
Collapse
Affiliation(s)
- Miguel A. Maria-Solano
- CompBioLab Group, Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Maria Aurèlia Capmany 69, Girona 17003, Spain
- Global AI Drug Discovery Center, College of Pharmacy and Graduate School of Pharmaceutical Science, Ewha Womans University, Seoul 03760, Republic of Korea
| | - Thomas Kinateder
- Institute of Biophysics and Physical Biochemistry, Regensburg Center for Biochemistry, University of Regensburg, Universitätsstrasse 31, Regensburg 93053, Germany
| | - Javier Iglesias-Fernández
- CompBioLab Group, Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Maria Aurèlia Capmany 69, Girona 17003, Spain
- Nostrum Biodiscovery, Carrer de Baldiri Reixac, 10-12, Barcelona 08028, Spain
| | - Reinhard Sterner
- Institute of Biophysics and Physical Biochemistry, Regensburg Center for Biochemistry, University of Regensburg, Universitätsstrasse 31, Regensburg 93053, Germany
| | - Sílvia Osuna
- CompBioLab Group, Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Maria Aurèlia Capmany 69, Girona 17003, Spain
- ICREA, Pg. Lluís Companys 23, Barcelona 08010, Spain
| |
Collapse
|
16
|
Ghosh RK, Hilario E, Liu V, Wang Y, Niks D, Holmes JB, Sakhrani VV, Mueller LJ, Dunn MF. Mutation of βGln114 to Ala Alters the Stabilities of Allosteric States in Tryptophan Synthase Catalysis. Biochemistry 2021; 60:3173-3186. [PMID: 34595921 PMCID: PMC9122093 DOI: 10.1021/acs.biochem.1c00383] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The tryptophan synthase (TS) bienzyme complexes found in bacteria, yeasts, and molds are pyridoxal 5'-phosphate (PLP)-requiring enzymes that synthesize l-Trp. In the TS catalytic cycle, switching between the open and closed states of the α- and β-subunits via allosteric interactions is key to the efficient conversion of 3-indole-d-glycerol-3'-phosphate and l-Ser to l-Trp. In this process, the roles played by β-site residues proximal to the PLP cofactor have not yet been fully established. βGln114 is one such residue. To explore the roles played by βQ114, we conducted a detailed investigation of the βQ114A mutation on the structure and function of tryptophan synthase. Initial steady-state kinetic and static ultraviolet-visible spectroscopic analyses showed the Q to A mutation impairs catalytic activity and alters the stabilities of intermediates in the β-reaction. Therefore, we conducted X-ray structural and solid-state nuclear magnetic resonance spectroscopic studies to compare the wild-type and βQ114A mutant enzymes. These comparisons establish that the protein structural changes are limited to the Gln to Ala replacement, the loss of hydrogen bonds among the side chains of βGln114, βAsn145, and βArg148, and the inclusion of waters in the cavity created by substitution of the smaller Ala side chain. Because the conformations of the open and closed allosteric states are not changed by the mutation, we hypothesize that the altered properties arise from the lost hydrogen bonds that alter the relative stabilities of the open (βT state) and closed (βR state) conformations of the β-subunit and consequently alter the distribution of intermediates along the β-subunit catalytic path.
Collapse
Affiliation(s)
- Rittik K. Ghosh
- Department of Biochemistry, University of California, Riverside, California, 92521 USA
| | - Eduardo Hilario
- Department of Chemistry, University of California, Riverside, California, 92521 USA
| | - Viktoriia Liu
- Department of Chemistry, University of California, Riverside, California, 92521 USA
| | - Yangyang Wang
- Department of Chemistry, University of California, Riverside, California, 92521 USA
| | - Dimitri Niks
- Department of Biochemistry, University of California, Riverside, California, 92521 USA
| | - Jacob B. Holmes
- Department of Chemistry, University of California, Riverside, California, 92521 USA
| | - Varun V. Sakhrani
- Department of Chemistry, University of California, Riverside, California, 92521 USA
| | - Leonard J. Mueller
- Department of Chemistry, University of California, Riverside, California, 92521 USA
| | - Michael F. Dunn
- Department of Biochemistry, University of California, Riverside, California, 92521 USA
| |
Collapse
|
17
|
Michalska K, Wellington S, Maltseva N, Jedrzejczak R, Selem-Mojica N, Rosas-Becerra LR, Barona-Gómez F, Hung DT, Joachimiak A. Catalytically impaired TrpA subunit of tryptophan synthase from Chlamydia trachomatis is an allosteric regulator of TrpB. Protein Sci 2021; 30:1904-1918. [PMID: 34107106 PMCID: PMC8376405 DOI: 10.1002/pro.4143] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 06/07/2021] [Accepted: 06/08/2021] [Indexed: 11/10/2022]
Abstract
Intracellular growth and pathogenesis of Chlamydia species is controlled by the availability of tryptophan, yet the complete biosynthetic pathway for l‐Trp is absent among members of the genus. Some representatives, however, preserve genes encoding tryptophan synthase, TrpAB – a bifunctional enzyme catalyzing the last two steps in l‐Trp synthesis. TrpA (subunit α) converts indole‐3‐glycerol phosphate into indole and glyceraldehyde‐3‐phosphate (α reaction). The former compound is subsequently used by TrpB (subunit β) to produce l‐Trp in the presence of l‐Ser and a pyridoxal 5′‐phosphate cofactor (β reaction). Previous studies have indicated that in Chlamydia, TrpA has lost its catalytic activity yet remains associated with TrpB to support the β reaction. Here, we provide detailed analysis of the TrpAB from C. trachomatis D/UW‐3/CX, confirming that accumulation of mutations in the active site of TrpA renders it enzymatically inactive, despite the conservation of the catalytic residues. We also show that TrpA remains a functional component of the TrpAB complex, increasing the activity of TrpB by four‐fold. The side chain of non‐conserved βArg267 functions as cation effector, potentially rendering the enzyme less susceptible to the solvent ion composition. The observed structural and functional changes detected herein were placed in a broader evolutionary and genomic context, allowing identification of these mutations in relation to their trp gene contexts in which they occur. Moreover, in agreement with the in vitro data, partial relaxation of purifying selection for TrpA, but not for TrpB, was detected, reinforcing a partial loss of TrpA functions during the course of evolution. PDB Code(s): 6V82;
Collapse
Affiliation(s)
- Karolina Michalska
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, Illinois, USA.,Structural Biology Center, X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, USA
| | - Samantha Wellington
- Department of Genetics, Broad Institute of MIT and Harvard, Cambridge, Massachusetts, USA
| | - Natalia Maltseva
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, Illinois, USA
| | - Robert Jedrzejczak
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, Illinois, USA
| | - Nelly Selem-Mojica
- Evolution of Metabolic Diversity Laboratory, Unidad de Genómica Avanzada (Langebio), Cinvestav, Mexico
| | - L Rodrigo Rosas-Becerra
- Evolution of Metabolic Diversity Laboratory, Unidad de Genómica Avanzada (Langebio), Cinvestav, Mexico
| | - Francisco Barona-Gómez
- Evolution of Metabolic Diversity Laboratory, Unidad de Genómica Avanzada (Langebio), Cinvestav, Mexico
| | - Deborah T Hung
- Department of Genetics, Broad Institute of MIT and Harvard, Cambridge, Massachusetts, USA
| | - Andrzej Joachimiak
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, Illinois, USA.,Structural Biology Center, X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, USA.,Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA
| |
Collapse
|
18
|
D'Amico RN, Bosken YK, O'Rourke KF, Murray AM, Admasu W, Chang CEA, Boehr DD. Substitution of a Surface-Exposed Residue Involved in an Allosteric Network Enhances Tryptophan Synthase Function in Cells. Front Mol Biosci 2021; 8:679915. [PMID: 34124159 PMCID: PMC8187860 DOI: 10.3389/fmolb.2021.679915] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 05/11/2021] [Indexed: 11/13/2022] Open
Abstract
Networks of noncovalent amino acid interactions propagate allosteric signals throughout proteins. Tryptophan synthase (TS) is an allosterically controlled bienzyme in which the indole product of the alpha subunit (αTS) is transferred through a 25 Å hydrophobic tunnel to the active site of the beta subunit (βTS). Previous nuclear magnetic resonance and molecular dynamics simulations identified allosteric networks in αTS important for its function. We show here that substitution of a distant, surface-exposed network residue in αTS enhances tryptophan production, not by activating αTS function, but through dynamically controlling the opening of the indole channel and stimulating βTS activity. While stimulation is modest, the substitution also enhances cell growth in a tryptophan-auxotrophic strain of Escherichia coli compared to complementation with wild-type αTS, emphasizing the biological importance of the network. Surface-exposed networks provide new opportunities in allosteric drug design and protein engineering, and hint at potential information conduits through which the functions of a metabolon or even larger proteome might be coordinated and regulated.
Collapse
Affiliation(s)
- Rebecca N D'Amico
- Department of Chemistry, The Pennsylvania State University, University Park, PA, United States
| | - Yuliana K Bosken
- Department of Chemistry, The University of California Riverside, Riverside, CA, United States
| | - Kathleen F O'Rourke
- Department of Chemistry, The Pennsylvania State University, University Park, PA, United States
| | - Alec M Murray
- Department of Chemistry, The Pennsylvania State University, University Park, PA, United States
| | - Woudasie Admasu
- Department of Chemistry, The Pennsylvania State University, University Park, PA, United States
| | - Chia-En A Chang
- Department of Chemistry, The University of California Riverside, Riverside, CA, United States
| | - David D Boehr
- Department of Chemistry, The Pennsylvania State University, University Park, PA, United States
| |
Collapse
|
19
|
Sakhrani VV, Hilario E, Caulkins BG, Hatcher-Skeers ME, Fan L, Dunn MF, Mueller LJ. Backbone assignments and conformational dynamics in the S. typhimurium tryptophan synthase α-subunit from solution-state NMR. JOURNAL OF BIOMOLECULAR NMR 2020; 74:341-354. [PMID: 32415580 PMCID: PMC7451264 DOI: 10.1007/s10858-020-00320-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Accepted: 05/07/2020] [Indexed: 06/11/2023]
Abstract
Backbone assignments for the isolated α-subunit of Salmonella typhimurium tryptophan synthase (TS) are reported based on triple resonance solution-state NMR experiments on a uniformly 2H,13C,15N-labeled sample. From the backbone chemical shifts, secondary structure and random coil index order parameters (RCI-S2) are predicted. Titration with the 3-indole-D-glycerol 3'-phosphate analog, N-(4'-trifluoromethoxybenzenesulfonyl)-2-aminoethyl phosphate (F9), leads to chemical shift perturbations indicative of conformational changes from which an estimate of the dissociation constant is obtained. Comparisons of the backbone chemical-shifts, RCI-S2 values, and site-specific relaxation times with and without F9 reveal allosteric changes including modulation in secondary structures and loop rigidity induced upon ligand binding. A comparison is made to the X-ray crystal structure of the α-subunit in the full TS αββα bi-enzyme complex and to two new X-ray crystal structures of the isolated TS α-subunit reported in this work.
Collapse
Affiliation(s)
- Varun V Sakhrani
- Department of Chemistry, University of California Riverside, Riverside, CA, 92521, USA
| | - Eduardo Hilario
- Department of Chemistry, University of California Riverside, Riverside, CA, 92521, USA
| | - Bethany G Caulkins
- Keck Science Department, Claremont McKenna, Pitzer, and Scripps Colleges, Claremont, CA, 91711, USA
| | - Mary E Hatcher-Skeers
- Keck Science Department, Claremont McKenna, Pitzer, and Scripps Colleges, Claremont, CA, 91711, USA
| | - Li Fan
- Department of Biochemistry, University of California Riverside, Riverside, CA, 92521, USA
| | - Michael F Dunn
- Department of Biochemistry, University of California Riverside, Riverside, CA, 92521, USA
| | - Leonard J Mueller
- Department of Chemistry, University of California Riverside, Riverside, CA, 92521, USA.
| |
Collapse
|
20
|
Michalska K, Chang C, Maltseva NI, Jedrzejczak R, Robertson GT, Gusovsky F, McCarren P, Schreiber SL, Nag PP, Joachimiak A. Allosteric inhibitors of Mycobacterium tuberculosis tryptophan synthase. Protein Sci 2020; 29:779-788. [PMID: 31930594 PMCID: PMC7020977 DOI: 10.1002/pro.3825] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 01/07/2020] [Accepted: 01/08/2020] [Indexed: 12/13/2022]
Abstract
Global dispersion of multidrug resistant bacteria is very common and evolution of antibiotic-resistance is occurring at an alarming rate, presenting a formidable challenge for humanity. The development of new therapeuthics with novel molecular targets is urgently needed. Current drugs primarily affect protein, nucleic acid, and cell wall synthesis. Metabolic pathways, including those involved in amino acid biosynthesis, have recently sparked interest in the drug discovery community as potential reservoirs of such novel targets. Tryptophan biosynthesis, utilized by bacteria but absent in humans, represents one of the currently studied processes with a therapeutic focus. It has been shown that tryptophan synthase (TrpAB) is required for survival of Mycobacterium tuberculosis in macrophages and for evading host defense, and therefore is a promising drug target. Here we present crystal structures of TrpAB with two allosteric inhibitors of M. tuberculosis tryptophan synthase that belong to sulfolane and indole-5-sulfonamide chemical scaffolds. We compare our results with previously reported structural and biochemical studies of another, azetidine-containing M. tuberculosis tryptophan synthase inhibitor. This work shows how structurally distinct ligands can occupy the same allosteric site and make specific interactions. It also highlights the potential benefit of targeting more variable allosteric sites of important metabolic enzymes.
Collapse
Affiliation(s)
- Karolina Michalska
- Center for Structural Genomics of Infectious Diseases, Consortium for Advanced Science and EngineeringUniversity of ChicagoChicagoIllinois
- Structural Biology Center, X‐ray Science DivisionArgonne National LaboratoryArgonneIllinois
| | - Changsoo Chang
- Center for Structural Genomics of Infectious Diseases, Consortium for Advanced Science and EngineeringUniversity of ChicagoChicagoIllinois
- Structural Biology Center, X‐ray Science DivisionArgonne National LaboratoryArgonneIllinois
| | - Natalia I. Maltseva
- Center for Structural Genomics of Infectious Diseases, Consortium for Advanced Science and EngineeringUniversity of ChicagoChicagoIllinois
- Structural Biology Center, X‐ray Science DivisionArgonne National LaboratoryArgonneIllinois
| | - Robert Jedrzejczak
- Center for Structural Genomics of Infectious Diseases, Consortium for Advanced Science and EngineeringUniversity of ChicagoChicagoIllinois
- Structural Biology Center, X‐ray Science DivisionArgonne National LaboratoryArgonneIllinois
| | - Gregory T. Robertson
- Colorado State UniversityMycobacteria Research Laboratories, Department of Microbiology, Immunology and PathologyFort CollinsColorado
| | | | | | | | - Partha P. Nag
- Broad Institute of MIT and HarvardCambridgeMassachusetts
| | - Andrzej Joachimiak
- Center for Structural Genomics of Infectious Diseases, Consortium for Advanced Science and EngineeringUniversity of ChicagoChicagoIllinois
- Structural Biology Center, X‐ray Science DivisionArgonne National LaboratoryArgonneIllinois
- Department of Biochemistry and Molecular BiologyUniversity of ChicagoChicagoIllinois
| |
Collapse
|
21
|
Teixeira CSS, Ramos MJ, Sousa SF, Cerqueira NMFSA. Solving the Catalytic Mechanism of Tryptophan Synthase: an Emergent Drug Target in the Treatment of Tuberculosis. ChemCatChem 2019. [DOI: 10.1002/cctc.201901505] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Carla S. Silva Teixeira
- UCIBIO@REQUIMTEBioSIMDepartamento de BiomedicinaFaculdade de MedicinaUniversidade do Porto Porto 4200-319 Portugal
| | - Maria J. Ramos
- UCIBIO@REQUIMTEDepartamento de Química e BioquímicaFaculdade de CiênciasUniversidade do Porto Porto 4169-007 Portugal
| | - Sérgio F. Sousa
- UCIBIO@REQUIMTEBioSIMDepartamento de BiomedicinaFaculdade de MedicinaUniversidade do Porto Porto 4200-319 Portugal
| | - Nuno M. F. S. A. Cerqueira
- UCIBIO@REQUIMTEBioSIMDepartamento de BiomedicinaFaculdade de MedicinaUniversidade do Porto Porto 4200-319 Portugal
| |
Collapse
|
22
|
Maria-Solano MA, Iglesias-Fernández J, Osuna S. Deciphering the Allosterically Driven Conformational Ensemble in Tryptophan Synthase Evolution. J Am Chem Soc 2019; 141:13049-13056. [DOI: 10.1021/jacs.9b03646] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Miguel A. Maria-Solano
- CompBioLab group, Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Girona 17003, Spain
| | - Javier Iglesias-Fernández
- CompBioLab group, Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Girona 17003, Spain
| | - Sílvia Osuna
- CompBioLab group, Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Girona 17003, Spain
- ICREA, Pg. Lluís Companys 23, Barcelona 08010, Spain
| |
Collapse
|
23
|
Michalska K, Gale J, Joachimiak G, Chang C, Hatzos-Skintges C, Nocek B, Johnston SE, Bigelow L, Bajrami B, Jedrzejczak RP, Wellington S, Hung DT, Nag PP, Fisher SL, Endres M, Joachimiak A. Conservation of the structure and function of bacterial tryptophan synthases. IUCRJ 2019; 6:649-664. [PMID: 31316809 PMCID: PMC6608616 DOI: 10.1107/s2052252519005955] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Accepted: 04/29/2019] [Indexed: 06/10/2023]
Abstract
Tryptophan biosynthesis is one of the most characterized processes in bacteria, in which the enzymes from Salmonella typhimurium and Escherichia coli serve as model systems. Tryptophan synthase (TrpAB) catalyzes the final two steps of tryptophan biosynthesis in plants, fungi and bacteria. This pyridoxal 5'-phosphate (PLP)-dependent enzyme consists of two protein chains, α (TrpA) and β (TrpB), functioning as a linear αββα heterotetrameric complex containing two TrpAB units. The reaction has a complicated, multistep mechanism resulting in the β-replacement of the hydroxyl group of l-serine with an indole moiety. Recent studies have shown that functional TrpAB is required for the survival of pathogenic bacteria in macrophages and for evading host defense. Therefore, TrpAB is a promising target for drug discovery, as its orthologs include enzymes from the important human pathogens Streptococcus pneumoniae, Legionella pneumophila and Francisella tularensis, the causative agents of pneumonia, legionnaires' disease and tularemia, respectively. However, specific biochemical and structural properties of the TrpABs from these organisms have not been investigated. To fill the important phylogenetic gaps in the understanding of TrpABs and to uncover unique features of TrpAB orthologs to spearhead future drug-discovery efforts, the TrpABs from L. pneumophila, F. tularensis and S. pneumoniae have been characterized. In addition to kinetic properties and inhibitor-sensitivity data, structural information gathered using X-ray crystallo-graphy is presented. The enzymes show remarkable structural conservation, but at the same time display local differences in both their catalytic and allosteric sites that may be responsible for the observed differences in catalysis and inhibitor binding. This functional dissimilarity may be exploited in the design of species-specific enzyme inhibitors.
Collapse
Affiliation(s)
- Karolina Michalska
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, IL 60367, USA
- Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Midwest Center for Structural Genomics, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Jennifer Gale
- Broad Institute of MIT and Harvard, Cambridge, MA 02141, USA
| | - Grazyna Joachimiak
- Midwest Center for Structural Genomics, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Changsoo Chang
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, IL 60367, USA
- Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Midwest Center for Structural Genomics, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Catherine Hatzos-Skintges
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, IL 60367, USA
| | - Boguslaw Nocek
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, IL 60367, USA
- Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Midwest Center for Structural Genomics, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | | | - Lance Bigelow
- Midwest Center for Structural Genomics, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Besnik Bajrami
- Broad Institute of MIT and Harvard, Cambridge, MA 02141, USA
| | - Robert P. Jedrzejczak
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, IL 60367, USA
- Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Midwest Center for Structural Genomics, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | | | - Deborah T. Hung
- Broad Institute of MIT and Harvard, Cambridge, MA 02141, USA
| | - Partha P. Nag
- Broad Institute of MIT and Harvard, Cambridge, MA 02141, USA
| | | | - Michael Endres
- Midwest Center for Structural Genomics, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Andrzej Joachimiak
- Center for Structural Genomics of Infectious Diseases, University of Chicago, Chicago, IL 60367, USA
- Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Midwest Center for Structural Genomics, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60367, USA
| |
Collapse
|
24
|
Gorman SD, D'Amico RN, Winston DS, Boehr DD. Engineering Allostery into Proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1163:359-384. [PMID: 31707711 PMCID: PMC7508002 DOI: 10.1007/978-981-13-8719-7_15] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Our ability to engineer protein structure and function has grown dramatically over recent years. Perhaps the next level in protein design is to develop proteins whose function can be regulated in response to various stimuli, including ligand binding, pH changes, and light. Endeavors toward these goals have tested and expanded on our understanding of protein function and allosteric regulation. In this chapter, we provide examples from different methods for developing new allosterically regulated proteins. These methods range from whole insertion of regulatory domains into new host proteins, to covalent attachment of photoswitches to generate light-responsive proteins, and to targeted changes to specific amino acid residues, especially to residues identified to be important for relaying allosteric information across the protein framework. Many of the examples we discuss have already found practical use in medical and biotechnology applications.
Collapse
Affiliation(s)
- Scott D Gorman
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
| | - Rebecca N D'Amico
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
| | - Dennis S Winston
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
| | - David D Boehr
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA.
| |
Collapse
|
25
|
Buller AR, van Roye P, Cahn JK, Scheele RA, Herger M, Arnold FH. Directed Evolution Mimics Allosteric Activation by Stepwise Tuning of the Conformational Ensemble. J Am Chem Soc 2018; 140:7256-7266. [PMID: 29712420 PMCID: PMC5999571 DOI: 10.1021/jacs.8b03490] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Allosteric enzymes contain a wealth of catalytic diversity that remains distinctly underutilized for biocatalysis. Tryptophan synthase is a model allosteric system and a valuable enzyme for the synthesis of noncanonical amino acids (ncAA). Previously, we evolved the β-subunit from Pyrococcus furiosus, PfTrpB, for ncAA synthase activity in the absence of its native partner protein PfTrpA. However, the precise mechanism by which mutation activated TrpB to afford a stand-alone catalyst remained enigmatic. Here, we show that directed evolution caused a gradual change in the rate-limiting step of the catalytic cycle. Concomitantly, the steady-state distribution of the intermediates shifts to favor covalently bound Trp adducts, which have increased thermodynamic stability. The biochemical properties of these evolved, stand-alone TrpBs converge on those induced in the native system by allosteric activation. High-resolution crystal structures of the wild-type enzyme, an intermediate in the lineage, and the final variant, encompassing five distinct chemical states, show that activating mutations have only minor structural effects on their immediate environment. Instead, mutation stabilizes the large-scale motion of a subdomain to favor an otherwise transiently populated closed conformational state. This increase in stability enabled the first structural description of Trp covalently bound in a catalytically active TrpB, confirming key features of catalysis. These data combine to show that sophisticated models of allostery are not a prerequisite to recapitulating its complex effects via directed evolution, opening the way to engineering stand-alone versions of diverse allosteric enzymes.
Collapse
Affiliation(s)
- Andrew R. Buller
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Ave, Madison, Wisconsin 53706, United States
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Paul van Roye
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Jackson K.B. Cahn
- Institute of Microbiology, Eidgenössische Technische Hochschule (ETH) Zürich, Vladimir-Prelog-Weg 4, Zurich 8093, Switzerland
| | - Remkes A. Scheele
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Michael Herger
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Frances H. Arnold
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| |
Collapse
|
26
|
Khan S, Farooq U, Kurnikova M. Protein stability and dynamics influenced by ligands in extremophilic complexes - a molecular dynamics investigation. MOLECULAR BIOSYSTEMS 2018; 13:1874-1887. [PMID: 28737816 DOI: 10.1039/c7mb00210f] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In this study, we explore the structural and dynamic adaptations of the Tryptophan synthase α-subunit in a ligand bound state in psychrophilic, mesophilic and hyperthermophilic organisms at different temperatures by MD simulations. We quantify the global and local fluctuations in the 40 ns time scale by analyzing the root mean square deviation/fluctuations. The distinct behavior of the active site and loop 6 is observed with the elevation of temperature. Protein stability relies more on electrostatic interactions, and these interactions might be responsible for the stability of varying temperature evolved proteins. The paper also focuses on the effect of temperature on protein dynamics and stability governed by the distinct behavior of the ligand associated with its retention, binding and dissociation over the course of time. The integration of principle component analysis and a free energy landscape was useful in identifying the conformational space accessible to ligand bound homologues and how the presence of the ligand alters the conformational and dynamic properties of the protein.
Collapse
Affiliation(s)
- Sara Khan
- Department of Chemistry, COMSATS Institute of Information Technology, Abbottabad-22060, Pakistan.
| | | | | |
Collapse
|
27
|
Boville CE, Romney DK, Almhjell PJ, Sieben M, Arnold FH. Improved Synthesis of 4-Cyanotryptophan and Other Tryptophan Analogues in Aqueous Solvent Using Variants of TrpB from Thermotoga maritima. J Org Chem 2018; 83:7447-7452. [PMID: 29651849 DOI: 10.1021/acs.joc.8b00517] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The use of enzymes has become increasingly widespread in synthesis as chemists strive to reduce their reliance on organic solvents in favor of more environmentally benign aqueous media. With this in mind, we previously endeavored to engineer the tryptophan synthase β-subunit (TrpB) for production of noncanonical amino acids that had previously been synthesized through multistep routes involving water-sensitive reagents. This enzymatic platform proved effective for the synthesis of analogues of the amino acid tryptophan (Trp), which are frequently used in pharmaceutical synthesis as well as chemical biology. However, certain valuable compounds, such as the blue fluorescent amino acid 4-cyanotryptophan (4-CN-Trp), could only be made in low yield, even at elevated temperature (75 °C). Here, we describe the engineering of TrpB from Thermotoga maritima that improved synthesis of 4-CN-Trp from 24% to 78% yield. Remarkably, although the final enzyme maintains high thermostability ( T50 = 93 °C), its temperature profile is shifted such that high reactivity is observed at ∼37 °C (76% yield), creating the possibility for in vivo 4-CN-Trp production. The improvements are not specific to 4-CN-Trp; a boost in activity at lower temperature is also demonstrated for other Trp analogues.
Collapse
Affiliation(s)
- Christina E Boville
- Division of Chemistry and Chemical Engineering 210-41 , California Institute of Technology , 1200 East California Boulevard , Pasadena , California 91125 , United States
| | - David K Romney
- Division of Chemistry and Chemical Engineering 210-41 , California Institute of Technology , 1200 East California Boulevard , Pasadena , California 91125 , United States
| | - Patrick J Almhjell
- Division of Chemistry and Chemical Engineering 210-41 , California Institute of Technology , 1200 East California Boulevard , Pasadena , California 91125 , United States
| | - Michaela Sieben
- Division of Chemistry and Chemical Engineering 210-41 , California Institute of Technology , 1200 East California Boulevard , Pasadena , California 91125 , United States
| | - Frances H Arnold
- Division of Chemistry and Chemical Engineering 210-41 , California Institute of Technology , 1200 East California Boulevard , Pasadena , California 91125 , United States
| |
Collapse
|
28
|
Romney DK, Murciano-Calles J, Wehrmüller JE, Arnold FH. Unlocking Reactivity of TrpB: A General Biocatalytic Platform for Synthesis of Tryptophan Analogues. J Am Chem Soc 2017; 139:10769-10776. [PMID: 28708383 DOI: 10.1021/jacs.7b05007/suppl_file/ja7b05007_si_002.pdf] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Derivatives of the amino acid tryptophan (Trp) serve as precursors for the chemical and biological synthesis of complex molecules with a wide range of biological properties. Trp analogues are also valuable as building blocks for medicinal chemistry and as tools for chemical biology. While the enantioselective synthesis of Trp analogues is often lengthy and requires the use of protecting groups, enzymes have the potential to synthesize such products in fewer steps and with the pristine chemo- and stereoselectivity that is a hallmark of biocatalysis. The enzyme TrpB is especially attractive because it can form Trp analogues directly from serine (Ser) and the corresponding indole analogue. However, many potentially useful substrates, including bulky or electron-deficient indoles, are poorly accepted. We have applied directed evolution to TrpB from Pyrococcus furiosus and Thermotoga maritima to generate a suite of catalysts for the synthesis of previously intractable Trp analogues. For the most challenging substrates, such as nitroindoles, the key to improving activity lay in the mutation of a universally conserved and mechanistically important residue, E104. The new catalysts express at high levels (>200 mg/L of Escherichia coli culture) and can be purified by heat treatment; they can operate up to 75 °C (where solubility is enhanced) and can synthesize enantiopure Trp analogues substituted at the 4-, 5-, 6-, and 7-positions, using Ser and readily available indole analogues as starting materials. Spectroscopic analysis shows that many of the activating mutations suppress the decomposition of the active electrophilic intermediate, an amino-acrylate, which aids in unlocking the synthetic potential of TrpB.
Collapse
Affiliation(s)
- David K Romney
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Javier Murciano-Calles
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Jöri E Wehrmüller
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Frances H Arnold
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| |
Collapse
|
29
|
Romney DK, Murciano-Calles J, Wehrmüller JE, Arnold FH. Unlocking Reactivity of TrpB: A General Biocatalytic Platform for Synthesis of Tryptophan Analogues. J Am Chem Soc 2017; 139:10769-10776. [PMID: 28708383 PMCID: PMC5589443 DOI: 10.1021/jacs.7b05007] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Derivatives
of the amino acid tryptophan (Trp) serve as precursors
for the chemical and biological synthesis of complex molecules with
a wide range of biological properties. Trp analogues are also valuable
as building blocks for medicinal chemistry and as tools for chemical
biology. While the enantioselective synthesis of Trp analogues is
often lengthy and requires the use of protecting groups, enzymes have
the potential to synthesize such products in fewer steps and with
the pristine chemo- and stereoselectivity that is a hallmark
of biocatalysis. The enzyme TrpB is especially attractive because
it can form Trp analogues directly from serine (Ser) and the corresponding
indole analogue. However, many potentially useful substrates, including
bulky or electron-deficient indoles, are poorly accepted. We have
applied directed evolution to TrpB from Pyrococcus furiosus and Thermotoga maritima to generate a suite of
catalysts for the synthesis of previously intractable Trp analogues.
For the most challenging substrates, such as nitroindoles, the key
to improving activity lay in the mutation of a universally conserved
and mechanistically important residue, E104. The new catalysts express
at high levels (>200 mg/L of Escherichia coli culture)
and can be purified by heat treatment; they can operate up to 75 °C
(where solubility is enhanced) and can synthesize enantiopure Trp
analogues substituted at the 4-, 5-, 6-, and 7-positions, using Ser
and readily available indole analogues as starting materials. Spectroscopic
analysis shows that many of the activating mutations suppress the
decomposition of the active electrophilic intermediate, an amino-acrylate,
which aids in unlocking the synthetic potential of TrpB.
Collapse
Affiliation(s)
- David K Romney
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Javier Murciano-Calles
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Jöri E Wehrmüller
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Frances H Arnold
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States
| |
Collapse
|
30
|
A small-molecule allosteric inhibitor of Mycobacterium tuberculosis tryptophan synthase. Nat Chem Biol 2017; 13:943-950. [PMID: 28671682 DOI: 10.1038/nchembio.2420] [Citation(s) in RCA: 85] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2017] [Accepted: 05/11/2017] [Indexed: 12/16/2022]
Abstract
New antibiotics with novel targets are greatly needed. Bacteria have numerous essential functions, but only a small fraction of such processes-primarily those involved in macromolecular synthesis-are inhibited by current drugs. Targeting metabolic enzymes has been the focus of recent interest, but effective inhibitors have been difficult to identify. We describe a synthetic azetidine derivative, BRD4592, that kills Mycobacterium tuberculosis (Mtb) through allosteric inhibition of tryptophan synthase (TrpAB), a previously untargeted, highly allosterically regulated enzyme. BRD4592 binds at the TrpAB α-β-subunit interface and affects multiple steps in the enzyme's overall reaction, resulting in inhibition not easily overcome by changes in metabolic environment. We show that TrpAB is required for the survival of Mtb and Mycobacterium marinum in vivo and that this requirement may be independent of an adaptive immune response. This work highlights the effectiveness of allosteric inhibition for targeting proteins that are naturally highly dynamic and that are essential in vivo, despite their apparent dispensability under in vitro conditions, and suggests a framework for the discovery of a next generation of allosteric inhibitors.
Collapse
|
31
|
Tang Z, Chang CEA. Systematic Dissociation Pathway Searches Guided by Principal Component Modes. J Chem Theory Comput 2017; 13:2230-2244. [PMID: 28418661 PMCID: PMC5920795 DOI: 10.1021/acs.jctc.6b01204] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We introduce a novel method, Pathway Search guided by Internal Motions (PSIM), that efficiently finds molecular dissociation pathways of a ligand-receptor system with guidance from principal component (PC) modes obtained from molecular dynamics (MD) simulations. Modeling ligand-receptor dissociation pathways can provide insights into molecular recognition and has practical applications, including understanding kinetic mechanisms and barriers to binding/unbinding as well as design of drugs with desired kinetic properties. PSIM uses PC modes in multilayer internal coordinates to identify natural molecular motions that guide the search for conformational switches and unbinding pathways. The new multilayer internal coordinates overcome problems with Cartesian and classical internal coordinates that fail to smoothly present dihedral rotation or generate nonphysical distortions. We used HIV-1 protease, which has large-scale flap motions, as an example protein to demonstrate use of the multilayer internal coordinates. We provide examples of algorithms and implementation of PSIM with alanine dipeptide and chemical host-guest systems, 2-naphthyl ethanol-β-cyclodextrin and tetramethylammonium-cryptophane complexes. Tetramethylammonium-cryptophane has slow binding/unbinding kinetics. Its residence time, the length to dissociate tetramethylammonium from the host, is ∼14 s from experiments, and PSIM revealed 4 dissociation pathways in approximately 150 CPU h. We also searched the releasing pathways for the product glyceraldehyde-3-phosphate from tryptophan synthase, and one complete dissociation pathway was constructed after running multiple search iterations in approximately 300 CPU h. With guidance by internal PC modes from MD simulations, the PSIM method has advantages over simulation-based methods to search for dissociation pathways of molecular systems with slow noncovalent kinetic behavior.
Collapse
Affiliation(s)
- Zhiye Tang
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Chia-en A. Chang
- Department of Chemistry, University of California, Riverside, California 92521, United States
| |
Collapse
|
32
|
Francis D, Winn M, Latham J, Greaney MF, Micklefield J. An Engineered Tryptophan Synthase Opens New Enzymatic Pathways to β-Methyltryptophan and Derivatives. Chembiochem 2017; 18:382-386. [PMID: 28005309 DOI: 10.1002/cbic.201600471] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Indexed: 01/23/2023]
Abstract
β-Methyltryptophans (β-mTrp) are precursors in the biosynthesis of bioactive natural products and are used in the synthesis of peptidomimetic-based therapeutics. Currently β-mTrp is produced by inefficient multistep synthetic methods. Here we demonstrate how an engineered variant of tryptophan synthase from Salmonella (StTrpS) can catalyse the efficient condensation of l-threonine and various indoles to generate β-mTrp and derivatives in a single step. Although l-serine is the natural substrate for TrpS, targeted mutagenesis of the StTrpS active site provided a variant (βL166V) that can better accommodate l-Thr as a substrate. The condensation of l-Thr and indole proceeds with retention of configuration at both α- and β-positions to give (2S,3S)-β-mTrp. The integration of StTrpS (βL166V) with l-amino acid oxidase, halogenase enzymes and palladium chemocatalysts provides access to further d-configured and regioselectively halogenated or arylated β-mTrp derivatives.
Collapse
Affiliation(s)
- Daniel Francis
- School of Chemistry, Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK
| | - Michael Winn
- School of Chemistry, Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK
| | - Jonathan Latham
- School of Chemistry, Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK
| | - Michael F Greaney
- School of Chemistry, Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK
| | - Jason Micklefield
- School of Chemistry, Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK
| |
Collapse
|
33
|
Buller AR, van Roye P, Murciano-Calles J, Arnold FH. Tryptophan Synthase Uses an Atypical Mechanism To Achieve Substrate Specificity. Biochemistry 2016; 55:7043-7046. [PMID: 27935677 PMCID: PMC5207025 DOI: 10.1021/acs.biochem.6b01127] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Tryptophan synthase (TrpS) catalyzes the final steps in the biosynthesis of l-tryptophan from l-serine (Ser) and indole-3-glycerol phosphate (IGP). We report that native TrpS can also catalyze a productive reaction with l-threonine (Thr), leading to (2S,3S)-β-methyltryptophan. Surprisingly, β-substitution occurs in vitro with a 3.4-fold higher catalytic efficiency for Ser over Thr using saturating indole, despite a >82000-fold preference for Ser in direct competition using IGP. Structural data identify a novel product binding site, and kinetic experiments clarify the atypical mechanism of specificity: Thr binds efficiently but decreases the affinity for indole and disrupts the allosteric signaling that regulates the catalytic cycle.
Collapse
Affiliation(s)
- Andrew R. Buller
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Paul van Roye
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Javier Murciano-Calles
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| | - Frances H. Arnold
- Division of Chemistry and Chemical Engineering 210-41, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States
| |
Collapse
|
34
|
Caulkins BG, Young RP, Kudla RA, Yang C, Bittbauer T, Bastin B, Hilario E, Fan L, Marsella MJ, Dunn MF, Mueller LJ. NMR Crystallography of a Carbanionic Intermediate in Tryptophan Synthase: Chemical Structure, Tautomerization, and Reaction Specificity. J Am Chem Soc 2016; 138:15214-15226. [PMID: 27779384 PMCID: PMC5129030 DOI: 10.1021/jacs.6b08937] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2016] [Indexed: 12/22/2022]
Abstract
Carbanionic intermediates play a central role in the catalytic transformations of amino acids performed by pyridoxal-5'-phosphate (PLP)-dependent enzymes. Here, we make use of NMR crystallography-the synergistic combination of solid-state nuclear magnetic resonance, X-ray crystallography, and computational chemistry-to interrogate a carbanionic/quinonoid intermediate analogue in the β-subunit active site of the PLP-requiring enzyme tryptophan synthase. The solid-state NMR chemical shifts of the PLP pyridine ring nitrogen and additional sites, coupled with first-principles computational models, allow a detailed model of protonation states for ionizable groups on the cofactor, substrates, and nearby catalytic residues to be established. Most significantly, we find that a deprotonated pyridine nitrogen on PLP precludes formation of a true quinonoid species and that there is an equilibrium between the phenolic and protonated Schiff base tautomeric forms of this intermediate. Natural bond orbital analysis indicates that the latter builds up negative charge at the substrate Cα and positive charge at C4' of the cofactor, consistent with its role as the catalytic tautomer. These findings support the hypothesis that the specificity for β-elimination/replacement versus transamination is dictated in part by the protonation states of ionizable groups on PLP and the reacting substrates and underscore the essential role that NMR crystallography can play in characterizing both chemical structure and dynamics within functioning enzyme active sites.
Collapse
Affiliation(s)
- Bethany G. Caulkins
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Robert P. Young
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Ryan A. Kudla
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Chen Yang
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Thomas
J. Bittbauer
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Baback Bastin
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Eduardo Hilario
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Li Fan
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Michael J. Marsella
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Michael F. Dunn
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Leonard J. Mueller
- Department of Chemistry, and Department of Biochemistry, University of California, Riverside, California 92521, United States
| |
Collapse
|
35
|
Murciano-Calles J, Romney DK, Brinkmann-Chen S, Buller AR, Arnold FH. A Panel of TrpB Biocatalysts Derived from Tryptophan Synthase through the Transfer of Mutations that Mimic Allosteric Activation. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201606242] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Javier Murciano-Calles
- Division of Chemistry and Chemical Engineering; California Institute of Technology; Pasadena CA 91125 USA
| | - David K. Romney
- Division of Chemistry and Chemical Engineering; California Institute of Technology; Pasadena CA 91125 USA
| | - Sabine Brinkmann-Chen
- Division of Chemistry and Chemical Engineering; California Institute of Technology; Pasadena CA 91125 USA
| | - Andrew R. Buller
- Division of Chemistry and Chemical Engineering; California Institute of Technology; Pasadena CA 91125 USA
| | - Frances H. Arnold
- Division of Chemistry and Chemical Engineering; California Institute of Technology; Pasadena CA 91125 USA
| |
Collapse
|
36
|
Murciano-Calles J, Romney DK, Brinkmann-Chen S, Buller AR, Arnold FH. A Panel of TrpB Biocatalysts Derived from Tryptophan Synthase through the Transfer of Mutations that Mimic Allosteric Activation. Angew Chem Int Ed Engl 2016; 55:11577-81. [PMID: 27510733 DOI: 10.1002/anie.201606242] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Indexed: 11/05/2022]
Abstract
Naturally occurring enzyme homologues often display highly divergent activity with non-natural substrates. Exploiting this diversity with enzymes engineered for new or altered function, however, is laborious because the engineering must be replicated for each homologue. A small set of mutations of the tryptophan synthase β-subunit (TrpB) from Pyrococcus furiosus, which mimics the activation afforded by binding of the α-subunit, was demonstrated to have a similar activating effect in different TrpB homologues with as little as 57 % sequence identity. Kinetic and spectroscopic analyses indicate that the mutations function through the same mechanism: mimicry of α-subunit binding. From these enzymes, we identified a new TrpB catalyst that displays a remarkably broad activity profile in the synthesis of 5-substituted tryptophans. This demonstrates that allosteric activation can be recapitulated throughout a protein family to explore natural sequence diversity for desirable biocatalytic transformations.
Collapse
Affiliation(s)
- Javier Murciano-Calles
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - David K Romney
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Sabine Brinkmann-Chen
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Andrew R Buller
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Frances H Arnold
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA.
| |
Collapse
|
37
|
Boulton S, Melacini G. Advances in NMR Methods To Map Allosteric Sites: From Models to Translation. Chem Rev 2016; 116:6267-304. [PMID: 27111288 DOI: 10.1021/acs.chemrev.5b00718] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The last five years have witnessed major developments in the understanding of the allosteric phenomenon, broadly defined as coupling between remote molecular sites. Such advances have been driven not only by new theoretical models and pharmacological applications of allostery, but also by progress in the experimental approaches designed to map allosteric sites and transitions. Among these techniques, NMR spectroscopy has played a major role given its unique near-atomic resolution and sensitivity to the dynamics that underlie allosteric couplings. Here, we highlight recent progress in the NMR methods tailored to investigate allostery with the goal of offering an overview of which NMR approaches are best suited for which allosterically relevant questions. The picture of the allosteric "NMR toolbox" is provided starting from one of the simplest models of allostery (i.e., the four-state thermodynamic cycle) and continuing to more complex multistate mechanisms. We also review how such an "NMR toolbox" has assisted the elucidation of the allosteric molecular basis for disease-related mutations and the discovery of novel leads for allosteric drugs. From this overview, it is clear that NMR plays a central role not only in experimentally validating transformative theories of allostery, but also in tapping the full translational potential of allosteric systems.
Collapse
Affiliation(s)
- Stephen Boulton
- Department of Chemistry and Chemical Biology Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main St. W., Hamilton L8S 4M1, Canada
| | - Giuseppe Melacini
- Department of Chemistry and Chemical Biology Department of Biochemistry and Biomedical Sciences, McMaster University , 1280 Main St. W., Hamilton L8S 4M1, Canada
| |
Collapse
|
38
|
Hilario E, Caulkins BG, Huang YMM, You W, Chang CEA, Mueller LJ, Dunn MF, Fan L. Visualizing the tunnel in tryptophan synthase with crystallography: Insights into a selective filter for accommodating indole and rejecting water. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1864:268-279. [PMID: 26708480 PMCID: PMC4732270 DOI: 10.1016/j.bbapap.2015.12.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Revised: 11/20/2015] [Accepted: 12/01/2015] [Indexed: 02/02/2023]
Abstract
Four new X-ray structures of tryptophan synthase (TS) crystallized with varying numbers of the amphipathic N-(4'-trifluoromethoxybenzoyl)-2-aminoethyl phosphate (F6) molecule are presented. These structures show one of the F6 ligands threaded into the tunnel from the β-site and reveal a distinct hydrophobic region. Over this expanse, the interactions between F6 and the tunnel are primarily nonpolar, while the F6 phosphoryl group fits into a polar pocket of the β-subunit active site. Further examination of TS structures reveals that one portion of the tunnel (T1) binds clusters of water molecules, whereas waters are not observed in the nonpolar F6 binding region of the tunnel (T2). MD simulation of another TS structure with an unobstructed tunnel also indicates the T2 region of the tunnel excludes water, consistent with a dewetted state that presents a significant barrier to the transfer of water into the closed β-site. We conclude that hydrophobic molecules can freely diffuse between the α- and β-sites via the tunnel, while water does not. We propose that exclusion of water serves to inhibit reaction of water with the α-aminoacrylate intermediate to form ammonium ion and pyruvate, a deleterious side reaction in the αβ-catalytic cycle. Finally, while most TS structures show βPhe280 partially blocking the tunnel between the α- and β-sites, new structures show an open tunnel, suggesting the flexibility of the βPhe280 side chain. Flexible docking studies and MD simulations confirm that the dynamic behavior of βPhe280 allows unhindered transfer of indole through the tunnel, therefore excluding a gating role for this residue.
Collapse
Affiliation(s)
- Eduardo Hilario
- Department of Biochemistry, University of California at Riverside, Riverside, CA 92521, USA
| | - Bethany G Caulkins
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA
| | - Yu-Ming M Huang
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA
| | - Wanli You
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA
| | - Chia-En A Chang
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA
| | - Leonard J Mueller
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, USA
| | - Michael F Dunn
- Department of Biochemistry, University of California at Riverside, Riverside, CA 92521, USA
| | - Li Fan
- Department of Biochemistry, University of California at Riverside, Riverside, CA 92521, USA
| |
Collapse
|
39
|
Young RP, Caulkins BG, Borchardt D, Bulloch DN, Larive CK, Dunn MF, Mueller LJ. Solution-State (17)O Quadrupole Central-Transition NMR Spectroscopy in the Active Site of Tryptophan Synthase. Angew Chem Int Ed Engl 2015; 55:1350-4. [PMID: 26661504 DOI: 10.1002/anie.201508898] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Indexed: 11/09/2022]
Abstract
Oxygen is an essential participant in the acid-base chemistry that takes place within many enzyme active sites, yet has remained virtually silent as a probe in NMR spectroscopy. Here, we demonstrate the first use of solution-state (17)O quadrupole central-transition NMR spectroscopy to characterize enzymatic intermediates under conditions of active catalysis. In the 143 kDa pyridoxal-5'-phosphate-dependent enzyme tryptophan synthase, reactions of the α-aminoacrylate intermediate with the nucleophiles indoline and 2-aminophenol correlate with an upfield shift of the substrate carboxylate oxygen resonances. First principles calculations suggest that the increased shieldings for these quinonoid intermediates result from the net increase in the charge density of the substrate-cofactor π-bonding network, particularly at the adjacent α-carbon site.
Collapse
Affiliation(s)
- Robert P Young
- Department of Chemistry, University of California, Riverside, Riverside, CA, 92521, USA
| | - Bethany G Caulkins
- Department of Chemistry, University of California, Riverside, Riverside, CA, 92521, USA
| | - Dan Borchardt
- Department of Chemistry, University of California, Riverside, Riverside, CA, 92521, USA
| | - Daryl N Bulloch
- Department of Chemistry, University of California, Riverside, Riverside, CA, 92521, USA
| | - Cynthia K Larive
- Department of Chemistry, University of California, Riverside, Riverside, CA, 92521, USA
| | - Michael F Dunn
- Department of Biochemistry, University of California, Riverside, Riverside, CA, 92521, USA
| | - Leonard J Mueller
- Department of Chemistry, University of California, Riverside, Riverside, CA, 92521, USA.
| |
Collapse
|
40
|
Young RP, Caulkins BG, Borchardt D, Bulloch DN, Larive CK, Dunn MF, Mueller LJ. Solution‐State
17
O Quadrupole Central‐Transition NMR Spectroscopy in the Active Site of Tryptophan Synthase. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201508898] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Robert P. Young
- Department of Chemistry University of California, Riverside Riverside CA 92521 USA
| | - Bethany G. Caulkins
- Department of Chemistry University of California, Riverside Riverside CA 92521 USA
| | - Dan Borchardt
- Department of Chemistry University of California, Riverside Riverside CA 92521 USA
| | - Daryl N. Bulloch
- Department of Chemistry University of California, Riverside Riverside CA 92521 USA
| | - Cynthia K. Larive
- Department of Chemistry University of California, Riverside Riverside CA 92521 USA
| | - Michael F. Dunn
- Department of Biochemistry University of California, Riverside Riverside CA 92521 USA
| | - Leonard J. Mueller
- Department of Chemistry University of California, Riverside Riverside CA 92521 USA
| |
Collapse
|
41
|
Directed evolution of the tryptophan synthase β-subunit for stand-alone function recapitulates allosteric activation. Proc Natl Acad Sci U S A 2015; 112:14599-604. [PMID: 26553994 DOI: 10.1073/pnas.1516401112] [Citation(s) in RCA: 94] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Enzymes in heteromeric, allosterically regulated complexes catalyze a rich array of chemical reactions. Separating the subunits of such complexes, however, often severely attenuates their catalytic activities, because they can no longer be activated by their protein partners. We used directed evolution to explore allosteric regulation as a source of latent catalytic potential using the β-subunit of tryptophan synthase from Pyrococcus furiosus (PfTrpB). As part of its native αββα complex, TrpB efficiently produces tryptophan and tryptophan analogs; activity drops considerably when it is used as a stand-alone catalyst without the α-subunit. Kinetic, spectroscopic, and X-ray crystallographic data show that this lost activity can be recovered by mutations that reproduce the effects of complexation with the α-subunit. The engineered PfTrpB is a powerful platform for production of Trp analogs and for further directed evolution to expand substrate and reaction scope.
Collapse
|
42
|
Huang YMM, You W, Caulkins BG, Dunn MF, Mueller LJ, Chang CEA. Protonation states and catalysis: Molecular dynamics studies of intermediates in tryptophan synthase. Protein Sci 2015; 25:166-83. [PMID: 26013176 DOI: 10.1002/pro.2709] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 05/13/2015] [Accepted: 05/14/2015] [Indexed: 12/13/2022]
Abstract
The importance of protonation states and proton transfer in pyridoxal 5'-phosphate (PLP)-chemistry can hardly be overstated. Although experimental approaches to investigate pKa values can provide general guidance for assigning proton locations, only static pictures of the chemical species are available. To obtain the overall protein dynamics for the interpretation of detailed enzyme catalysis in this study, guided by information from solid-state NMR, we performed molecular dynamics (MD) simulations for the PLP-dependent enzyme tryptophan synthase (TRPS), whose catalytic mechanism features multiple quasi-stable intermediates. The primary objective of this work is to elucidate how the position of a single proton on the reacting substrate affects local and global protein dynamics during the catalytic cycle. In general, proteins create a chemical environment and an ensemble of conformational motions to recognize different substrates with different protonations. The study of these interactions in TRPS shows that functional groups on the reacting substrate, such as the phosphoryl group, pyridine nitrogen, phenolic oxygen and carboxyl group, of each PLP-bound intermediate play a crucial role in constructing an appropriate molecular interface with TRPS. In particular, the protonation states of the ionizable groups on the PLP cofactor may enhance or weaken the attractions between the enzyme and substrate. In addition, remodulation of the charge distribution for the intermediates may help generate a suitable environment for chemical reactions. The results of our study enhance knowledge of protonation states for several PLP intermediates and help to elucidate their effects on protein dynamics in the function of TRPS and other PLP-dependent enzymes.
Collapse
Affiliation(s)
- Yu-Ming M Huang
- Department of Chemistry, University of California, Riverside, California, 92521
| | - Wanli You
- Department of Chemistry, University of California, Riverside, California, 92521
| | - Bethany G Caulkins
- Department of Chemistry, University of California, Riverside, California, 92521
| | - Michael F Dunn
- Department of Biochemistry, University of California, Riverside, California, 92521
| | - Leonard J Mueller
- Department of Chemistry, University of California, Riverside, California, 92521
| | - Chia-En A Chang
- Department of Chemistry, University of California, Riverside, California, 92521
| |
Collapse
|
43
|
Hartman JD, Neubauer TJ, Caulkins BG, Mueller LJ, Beran GJO. Converging nuclear magnetic shielding calculations with respect to basis and system size in protein systems. JOURNAL OF BIOMOLECULAR NMR 2015; 62:327-40. [PMID: 25993979 PMCID: PMC4512207 DOI: 10.1007/s10858-015-9947-2] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Accepted: 05/12/2015] [Indexed: 05/25/2023]
Abstract
Ab initio chemical shielding calculations greatly facilitate the interpretation of nuclear magnetic resonance (NMR) chemical shifts in biological systems, but the large sizes of these systems requires approximations in the chemical models used to represent them. Achieving good convergence in the predicted chemical shieldings is necessary before one can unravel how other complex structural and dynamical factors affect the NMR measurements. Here, we investigate how to balance trade-offs between using a better basis set or a larger cluster model for predicting the chemical shieldings of the substrates in two representative examples of protein-substrate systems involving different domains in tryptophan synthase: the N-(4'-trifluoromethoxybenzoyl)-2-aminoethyl phosphate (F9) ligand which binds in the α active site, and the 2-aminophenol quinonoid intermediate formed in the β active site. We first demonstrate that a chemically intuitive three-layer, locally dense basis model that uses a large basis on the substrate, a medium triple-zeta basis to describe its hydrogen-bonding partners and/or surrounding van der Waals cavity, and a crude basis set for more distant atoms provides chemical shieldings in good agreement with much more expensive large basis calculations. Second, long-range quantum mechanical interactions are important, and one can accurately estimate them as a small-basis correction to larger-basis calculations on a smaller cluster. The combination of these approaches enables one to perform density functional theory NMR chemical shift calculations in protein systems that are well-converged with respect to both basis set and cluster size.
Collapse
Affiliation(s)
- Joshua D. Hartman
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, Tel.: +1-951-827-7869
| | - Thomas J. Neubauer
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, Tel.: +1-951-827-7869
| | - Bethany G. Caulkins
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, Tel.: +1-951-827-7869
| | - Leonard J. Mueller
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, Tel.: +1-951-827-7869
| | - Gregory J. O. Beran
- Department of Chemistry, University of California at Riverside, Riverside, CA 92521, Tel.: +1-951-827-7869
| |
Collapse
|
44
|
Huang YMM, Kang M, Chang CEA. Switches of hydrogen bonds during ligand-protein association processes determine binding kinetics. J Mol Recognit 2015; 27:537-48. [PMID: 25042708 DOI: 10.1002/jmr.2377] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Revised: 03/22/2014] [Accepted: 03/24/2014] [Indexed: 11/05/2022]
Abstract
Revealing the processes of ligand-protein associations deepens our understanding of molecular recognition and binding kinetics. Hydrogen bonds (H-bonds) play a crucial role in optimizing ligand-protein interactions and ligand specificity. In addition to the formation of stable H-bonds in the final bound state, the formation of transient H-bonds during binding processes contributes binding kinetics that define a ligand as a fast or slow binder, which also affects drug action. However, the effect of forming the transient H-bonds on the kinetic properties is little understood. Guided by results from coarse-grained Brownian dynamics simulations, we used classical molecular dynamics simulations in an implicit solvent model and accelerated molecular dynamics simulations in explicit waters to show that the position and distribution of the H-bond donor or acceptor of a drug result in switching intermolecular and intramolecular H-bond pairs during ligand recognition processes. We studied two major types of HIV-1 protease ligands: a fast binder, xk263, and a slow binder, ritonavir. The slow association rate in ritonavir can be attributed to increased flexibility of ritonavir, which yields multistep transitions and stepwise entering patterns and the formation and breaking of complex H-bond pairs during the binding process. This model suggests the importance of conversions of spatiotemporal H-bonds during the association of ligands and proteins, which helps in designing inhibitors with preferred binding kinetics.
Collapse
Affiliation(s)
- Yu-ming M Huang
- Department of Chemistry, University of California, Riverside, CA, 92521, USA
| | | | | |
Collapse
|
45
|
Eginton C, Cressman WJ, Bachas S, Wade H, Beckett D. Allosteric coupling via distant disorder-to-order transitions. J Mol Biol 2015; 427:1695-704. [PMID: 25746672 DOI: 10.1016/j.jmb.2015.02.021] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Revised: 02/12/2015] [Accepted: 02/26/2015] [Indexed: 10/23/2022]
Abstract
Intrinsic disorder provides a means of maximizing allosteric coupling in proteins. However, the mechanisms by which the disorder functions in allostery remain to be elucidated. Small ligand, bio-5'-AMP, binding and dimerization of the Escherichia coli biotin repressor are allosterically coupled. Folding of a disordered loop in the allosteric effector binding site is required to realize the full coupling free energy of -4.0 ± 0.3 kcal/mol observed in the wild-type protein. Alanine substitution of a glycine residue on the dimerization surface that does not directly contribute to the dimerization interface completely abolishes this coupling. In this work, the structure of this variant, solved by X-ray crystallography, reveals a monomeric corepressor-bound protein. In the structure loops, neither of which contains the alanine substitution, on both the dimerization and effector binding surfaces that are folded in the corepressor-bound wild-type protein are disordered. The structural data combined with functional measurements indicate that allosteric coupling between ligand binding and dimerization in BirA (E. coli biotin repressor/biotin protein ligase) is achieved via reciprocal communication of disorder-to-order transitions on two distant functional surfaces.
Collapse
Affiliation(s)
- Christopher Eginton
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA
| | - William J Cressman
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA
| | - Sharrol Bachas
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
| | - Herschel Wade
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
| | - Dorothy Beckett
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA.
| |
Collapse
|
46
|
Catalytic roles of βLys87 in tryptophan synthase: (15)N solid state NMR studies. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2015; 1854:1194-9. [PMID: 25688830 DOI: 10.1016/j.bbapap.2015.02.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Revised: 02/06/2015] [Accepted: 02/09/2015] [Indexed: 10/24/2022]
Abstract
The proposed mechanism for tryptophan synthase shows βLys87 playing multiple catalytic roles: it bonds to the PLP cofactor, activates C4' for nucleophilic attack via a protonated Schiff base nitrogen, and abstracts and returns protons to PLP-bound substrates (i.e. acid-base catalysis). ε-¹⁵N-lysine TS was prepared to access the protonation state of βLys87 using ¹⁵N solid-state nuclear magnetic resonance (SSNMR) spectroscopy for three quasi-stable intermediates along the reaction pathway. These experiments establish that the protonation state of the ε-amino group switches between protonated and neutral states as the β-site undergoes conversion from one intermediate to the next during catalysis, corresponding to mechanistic steps where this lysine residue has been anticipated to play alternating acid and base catalytic roles that help steer reaction specificity in tryptophan synthase catalysis. This article is part of a Special Issue entitled: Cofactor-dependent proteins: evolution, chemical diversity and bio-applications. Guest Editors: Andrea Mozzarelli and Loredano Pollegioni.
Collapse
|
47
|
Caulkins B, Bastin B, Yang C, Neubauer TJ, Young RP, Hilario E, Huang YMM, Chang CEA, Fan L, Dunn MF, Marsella MJ, Mueller LJ. Protonation states of the tryptophan synthase internal aldimine active site from solid-state NMR spectroscopy: direct observation of the protonated Schiff base linkage to pyridoxal-5'-phosphate. J Am Chem Soc 2014; 136:12824-7. [PMID: 25148001 PMCID: PMC4183654 DOI: 10.1021/ja506267d] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2014] [Indexed: 11/29/2022]
Abstract
The acid-base chemistry that drives catalysis in pyridoxal-5'-phosphate (PLP)-dependent enzymes has been the subject of intense interest and investigation since the initial identification of PLP's role as a coenzyme in this extensive class of enzymes. It was first proposed over 50 years ago that the initial step in the catalytic cycle is facilitated by a protonated Schiff base form of the holoenzyme in which the linking lysine ε-imine nitrogen, which covalently binds the coenzyme, is protonated. Here we provide the first (15)N NMR chemical shift measurements of such a Schiff base linkage in the resting holoenzyme form, the internal aldimine state of tryptophan synthase. Double-resonance experiments confirm the assignment of the Schiff base nitrogen, and additional (13)C, (15)N, and (31)P chemical shift measurements of sites on the PLP coenzyme allow a detailed model of coenzyme protonation states to be established.
Collapse
Affiliation(s)
- Bethany
G. Caulkins
- Department
of Chemistry, University of California, Riverside, California 92521, United States
| | - Baback Bastin
- Department
of Chemistry, University of California, Riverside, California 92521, United States
| | - Chen Yang
- Department
of Chemistry, University of California, Riverside, California 92521, United States
| | - Thomas J. Neubauer
- Department
of Chemistry, University of California, Riverside, California 92521, United States
| | - Robert P. Young
- Department
of Chemistry, University of California, Riverside, California 92521, United States
| | - Eduardo Hilario
- Department
of Biochemistry, University of California, Riverside, California 92521, United States
| | - Yu-ming M. Huang
- Department
of Chemistry, University of California, Riverside, California 92521, United States
| | - Chia-en A. Chang
- Department
of Chemistry, University of California, Riverside, California 92521, United States
| | - Li Fan
- Department
of Biochemistry, University of California, Riverside, California 92521, United States
| | - Michael F. Dunn
- Department
of Biochemistry, University of California, Riverside, California 92521, United States
| | - Michael J. Marsella
- Department
of Chemistry, University of California, Riverside, California 92521, United States
| | - Leonard J. Mueller
- Department
of Chemistry, University of California, Riverside, California 92521, United States
| |
Collapse
|