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Hiefinger C, Mandl S, Wieland M, Kneuttinger A. Rational design, production and in vitro analysis of photoxenoproteins. Methods Enzymol 2023; 682:247-288. [PMID: 36948704 DOI: 10.1016/bs.mie.2022.12.003] [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: 01/20/2023]
Abstract
In synthetic biology, the artificial control of proteins by light is of growing interest since it enables the spatio-temporal regulation of downstream molecular processes. This precise photocontrol can be established by the site-directed incorporation of photo-sensitive non-canonical amino acids (ncAAs) into proteins, which generates so-called photoxenoproteins. Photoxenoproteins can be engineered using ncAAs that facilitate the irreversible activation or reversible regulation of their activity upon irradiation. In this chapter, we provide a general outline of the engineering process based on the current methodological state-of-the-art to obtain artificial photocontrol in proteins using the ncAAs o-nitrobenzyl-O-tyrosine as example for photocaged ncAAs (irreversible), and phenylalanine-4'-azobenzene as example for photoswitchable ncAAs (reversible). We thereby focus on the initial design as well as the production and characterization of photoxenoproteins in vitro. Finally, we outline the analysis of photocontrol under steady-state and non-steady-state conditions using the allosteric enzyme complexes imidazole glycerol phosphate synthase and tryptophan synthase as examples.
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Affiliation(s)
- Caroline Hiefinger
- Institute of Biophysics and Physical Biochemistry & Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany
| | - Sabrina Mandl
- Institute of Biophysics and Physical Biochemistry & Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany
| | - Mona Wieland
- Institute of Biophysics and Physical Biochemistry & Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany
| | - Andrea Kneuttinger
- Institute of Biophysics and Physical Biochemistry & Regensburg Center for Biochemistry, University of Regensburg, Regensburg, Germany.
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2
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Kneuttinger AC, Zwisele S, Straub K, Bruckmann A, Busch F, Kinateder T, Gaim B, Wysocki VH, Merkl R, Sterner R. Light-Regulation of Tryptophan Synthase by Combining Protein Design and Enzymology. Int J Mol Sci 2019; 20:E5106. [PMID: 31618845 PMCID: PMC6829457 DOI: 10.3390/ijms20205106] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Revised: 10/11/2019] [Accepted: 10/12/2019] [Indexed: 01/24/2023] Open
Abstract
The spatiotemporal control of enzymes by light is of growing importance for industrial biocatalysis. Within this context, the photo-control of allosteric interactions in enzyme complexes, common to practically all metabolic pathways, is particularly relevant. A prominent example of a metabolic complex with a high application potential is tryptophan synthase from Salmonella typhimurium (TS), in which the constituting TrpA and TrpB subunits mutually stimulate each other via a sophisticated allosteric network. To control TS allostery with light, we incorporated the unnatural amino acid o-nitrobenzyl-O-tyrosine (ONBY) at seven strategic positions of TrpA and TrpB. Initial screening experiments showed that ONBY in position 58 of TrpA (aL58ONBY) inhibits TS activity most effectively. Upon UV irradiation, ONBY decages to tyrosine, largely restoring the capacity of TS. Biochemical characterization, extensive steady-state enzyme kinetics, and titration studies uncovered the impact of aL58ONBY on the activities of TrpA and TrpB and identified reaction conditions under which the influence of ONBY decaging on allostery reaches its full potential. By applying those optimal conditions, we succeeded to directly light-activate TS(aL58ONBY) by a factor of ~100. Our findings show that rational protein design with a photo-sensitive unnatural amino acid combined with extensive enzymology is a powerful tool to fine-tune allosteric light-activation of a central metabolic enzyme complex.
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Affiliation(s)
- Andrea C Kneuttinger
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
| | - Stefanie Zwisele
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
| | - Kristina Straub
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
| | - Astrid Bruckmann
- Institute of Biochemistry, Genetics and Microbiology, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
| | - Florian Busch
- Department of Chemistry and Biochemistry and Resource for Native Mass Spectrometry Guided Structural Biology, The Ohio State University, Columbus, OH 43210, USA.
| | - Thomas Kinateder
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
| | - Barbara Gaim
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
| | - Vicki H Wysocki
- Department of Chemistry and Biochemistry and Resource for Native Mass Spectrometry Guided Structural Biology, The Ohio State University, Columbus, OH 43210, USA.
| | - Rainer Merkl
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
| | - Reinhard Sterner
- Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
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3
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Hardin A, Villalta CF, Doan M, Jabri M, Chockalingham V, White SJ, Fowler RG. A molecular characterization of spontaneous frameshift mutagenesis within the trpA gene of Escherichia coli. DNA Repair (Amst) 2007; 6:177-89. [PMID: 17084112 PMCID: PMC1804121 DOI: 10.1016/j.dnarep.2006.09.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2006] [Revised: 09/05/2006] [Accepted: 09/25/2006] [Indexed: 10/24/2022]
Abstract
Spontaneous frameshift mutations are an important source of genetic variation in all species and cause a large number of genetic disorders in humans. To enhance our understanding of the molecular mechanisms of frameshift mutagenesis, 583 spontaneous Trp+ revertants of two trpA frameshift alleles in Escherichia coli were isolated and DNA sequenced. In order to measure the contribution of methyl-directed mismatch repair to frameshift production, mutational spectra were constructed for both mismatch repair-proficient and repair-defective strains. The molecular origins of practically all of the frameshifts analyzed could be explained by one of six simple models based upon misalignment of the template or nascent DNA strands with or without misincorporation of primer nucleotides during DNA replication. Most frameshifts occurred within mononucleotide runs as has been shown often in previous studies but the location of the 76 frameshift sites was usually outside of runs. Mismatch repair generally was most effective in preventing the occurrence of frameshifts within runs but there was much variation from site to site. Most frameshift sites outside of runs appear to be refractory to mismatch repair although the small number of occurrences at most of these sites make firm conclusions impossible. There was a dense pattern of reversion sites within the trpA DNA region where reversion events could occur, suggesting that, in general, most DNA sequences are capable of undergoing spontaneous mutational events during replication that can lead to small deletions and insertions. Many of these errors are likely to occur at low frequencies and be tolerated as events too costly to prevent or repair. These studies also revealed an unpredicted flexibility in the primary amino acid sequence of the trpA product, the alpha subunit of tryptophan synthase.
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Affiliation(s)
- Aaron Hardin
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
| | | | - Michael Doan
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
| | - Mouna Jabri
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
| | | | - Steven J. White
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
| | - Robert G. Fowler
- Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
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4
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Spyrakis F, Raboni S, Cozzini P, Bettati S, Mozzarelli A. Allosteric communication between alpha and beta subunits of tryptophan synthase: modelling the open-closed transition of the alpha subunit. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2006; 1764:1102-9. [PMID: 16737856 DOI: 10.1016/j.bbapap.2006.03.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Revised: 03/16/2006] [Accepted: 03/16/2006] [Indexed: 12/12/2022]
Abstract
Ligand binding to the alpha-subunit of the alpha2beta2 complex of tryptophan synthase induces the alphaloop6 closure over the alpha-active site. This conformational change is associated with the formation of a hydrogen bond between alphaGly181 NH group and betaSer178 carbonyl oxygen, a key event for the triggering of intersubunit allosteric signals. Mutation of betaSer178 to Pro and alphaGly181 to Pro, Ala, Phe and Val abolishes the ligand-induced intersubunit communication. Molecular dynamics methods were applied to simulate the conformation of the highly flexible and crystallographically undetectable open state of alphaloop6 in the wild type and in the alpha181 mutants. The open conformation of alphaloop6 is favoured in the wild type enzyme in the absence of alpha-ligands, and in the alpha181 mutants both in the presence and absence of bound ligands. A very good correlation was found between the extent of limited tryptic proteolysis and both the hydrogen bond distance between alphaX181 and betaSer178, obtained from the molecular dynamics simulation, and the hydrogen bond strength, evaluated by HINT, an empirical force field that takes into account both enthalpic and entropic contributions. Comparison of the open and closed conformations of alphaloop6 suggests a pathway for substrate entrance into the alpha-active site and provides an explanation for the limited catalytic efficiency of the open state.
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Affiliation(s)
- Francesca Spyrakis
- Department of Biochemistry and Molecular Biology, University of Parma, 43100 Parma, Italy
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5
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Raboni S, Bettati S, Mozzarelli A. Identification of the geometric requirements for allosteric communication between the alpha- and beta-subunits of tryptophan synthase. J Biol Chem 2005; 280:13450-6. [PMID: 15691828 DOI: 10.1074/jbc.m414521200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The pyridoxal 5'-phosphate-dependent tryptophan synthase alpha2beta2 complex is a paradigmatic protein for substrate channeling and allosteric regulation. The enzymatic activity is modulated by a ligand-mediated equilibrium between open (inactive) and closed (active) conformations of the alpha- and beta-subunit, predominantly involving the mobile alpha loop 6 and the beta-COMM domain that contains beta helix 6. The alpha ligand-triggered intersubunit communication seems to rely on a single hydrogen bond formed between the carbonyl oxygen of betaSer-178 of beta helix 6 and the NH group of alphaGly-181 of alpha loop 6. We investigated whether and to what extent mutations of alphaGly-181 and betaSer-178 affect allosteric regulation by the replacement of betaSer-178 with Pro or Ala and of alphaGly-181 with either Pro to remove the amidic proton that forms the hydrogen bond or Ala, Val, and Phe to analyze the dependence on steric hindrance of the open-closed conformational transition. The alpha and beta activity assays and the equilibrium distribution of beta-subunit catalytic intermediates indicate that mutations do not significantly influence the intersubunit catalytic activation but completely abolish ligand-induced alpha-to beta-subunit signaling, demonstrating distinct pathways for alpha-beta-site communication. Limited proteolysis experiments indicate that the removal of the interaction between betaSer-178 and alphaGly-181 strongly favors the more trypsin-accessible open conformation of the alpha-active site. When the hydrogen bond cannot be formed, the alpha-subunit is unable to attain the closed conformation, and consequently, the allosteric signal is aborted at the subunit interface.
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Affiliation(s)
- Samanta Raboni
- Department of Biochemistry and Molecular Biology, University of Parma, 43100 Parma, Italy
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6
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Wood H, Roshick C, McClarty G. Tryptophan recycling is responsible for the interferon-gamma resistance of Chlamydia psittaci GPIC in indoleamine dioxygenase-expressing host cells. Mol Microbiol 2004; 52:903-16. [PMID: 15101993 DOI: 10.1111/j.1365-2958.2004.04029.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Comparative genomics indicates that vast differences in Chlamydia sp. host range and disease characteristics can be traced back to subtle variations in gene content within a region of the chromosome termed the plasticity zone. Genes required for tryptophan biosynthesis are located in the plasticity zone; however, the complement of genes encoded varies depending on the chlamydial species examined. Of the sequenced chlamydia genomes, Chlamydia psittaci GPIC contains the most complete tryptophan biosynthesis operon, encoding trpRDCFBA. Immediately downstream of the trp operon are genes encoding kynureninase and ribose phosphate pyrophosphokinase. Here, we show that, in GPIC, these genes are transcribed as a single transcript, the expression of which is regulated by tryptophan. Complementation analyses, using various mutant Escherichia coli isolates, indicate that the tryptophan biosynthesis, kynureninase and ribose phosphate pyrophosphokinase gene products are functional. Furthermore, growth of C. psittaci GPIC in HeLa cells, cultured in tryptophan-free medium, could be rescued by the addition of anthranilate, kynurenine or indole. In total, our results indicate that this complement of genes enables GPIC to recycle tryptophan and thus accounts for the interferon-gamma resistant phenotype displayed in indoleamine-2,3-dioxygenase-expressing host cells.
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Affiliation(s)
- Heidi Wood
- National Microbiology Laboratory, Health Canada, 1015 Arlington Street, Winnipeg, Manitoba, R3E 3R2
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7
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Gage MJ, Robinson AS. C-terminal hydrophobic interactions play a critical role in oligomeric assembly of the P22 tailspike trimer. Protein Sci 2003; 12:2732-47. [PMID: 14627734 PMCID: PMC2366982 DOI: 10.1110/ps.03150303] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2003] [Revised: 09/08/2003] [Accepted: 09/08/2003] [Indexed: 10/26/2022]
Abstract
The tailspike protein from the bacteriophage P22 is a well characterized model system for folding and assembly of multimeric proteins. Folding intermediates from both the in vivo and in vitro pathways have been identified, and both the initial folding steps and the protrimer-to-trimer transition have been well studied. In contrast, there has been little experimental evidence to describe the assembly of the protrimer. Previous results indicated that the C terminus plays a critical role in the overall stability of the P22 tailspike protein. Here, we present evidence that the C terminus is also the critical assembly point for trimer assembly. Three truncations of the full-length tailspike protein, TSPDeltaN, TSPDeltaC, and TSPDeltaNC, were generated and tested for their ability to form mixed trimer species. TSPDeltaN forms mixed trimers with full-length P22 tailspike, but TSPDeltaC and TSPDeltaNC are incapable of forming similar mixed trimer species. In addition, mutations in the hydrophobic core of the C terminus were unable to form trimer in vivo. Finally, the hydrophobic-binding dye ANS inhibits the formation of trimer by inhibiting progression through the folding pathway. Taken together, these results suggest that hydrophobic interactions between C-terminal regions of P22 tailspike monomers play a critical role in the assembly of the P22 tailspike trimer.
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Affiliation(s)
- Matthew J Gage
- Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716, USA
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8
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Abstract
Tryptophan synthase is a classic enzyme that channels a metabolic intermediate, indole. The crystal structure of the tryptophan synthase alpha2beta2 complex from Salmonella typhimurium revealed for the first time the architecture of a multienzyme complex and the presence of an intramolecular tunnel. This remarkable hydrophobic tunnel provides a likely passageway for indole from the active site of the alpha subunit, where it is produced, to the active site of the beta subunit, where it reacts with L-serine to form L-tryptophan in a pyridoxal phosphate-dependent reaction. Rapid kinetic studies of the wild type enzyme and of channel-impaired mutant enzymes provide strong evidence for the proposed channeling mechanism. Structures of a series of enzyme-substrate intermediates at the alpha and beta active sites are elucidating enzyme mechanisms and dynamics. These structural results are providing a fascinating picture of loops opening and closing, of domain movements, and of conformational changes in the indole tunnel. Solution studies provide further evidence for ligand-induced conformational changes that send signals between the alpha and beta subunits. The combined results show that the switching of the enzyme between open and closed conformations couples the catalytic reactions at the alpha and beta active sites and prevents the escape of indole.
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Affiliation(s)
- E W Miles
- Section on Enzyme Structure and Function, Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda Maryland 20892-0830, USA.
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9
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Kulik V, Weyand M, Seidel R, Niks D, Arac D, Dunn MF, Schlichting I. On the role of alphaThr183 in the allosteric regulation and catalytic mechanism of tryptophan synthase. J Mol Biol 2002; 324:677-90. [PMID: 12460570 DOI: 10.1016/s0022-2836(02)01109-9] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The catalytic activity and substrate channeling of the pyridoxal 5'-phosphate-dependent tryptophan synthase alpha(2)beta(2) complex is regulated by allosteric interactions that modulate the switching of the enzyme between open, low activity and closed, high activity states during the catalytic cycle. The highly conserved alphaThr183 residue is part of loop alphaL6 and is located next to the alpha-active site and forms part of the alpha-beta subunit interface. The role of the interactions of alphaThr183 in alpha-site catalysis and allosteric regulation was investigated by analyzing the kinetics and crystal structures of the isosteric mutant alphaThr183Val. The mutant displays strongly impaired allosteric alpha-beta communication, and the catalytic activity of the alpha-reaction is reduced one hundred fold, whereas the beta-activity is not affected. The structural work establishes that the basis for the missing inter-subunit signaling is the lack of loop alphaL6 closure even in the presence of the alpha-subunit ligands, 3-indolyl-D-glycerol 3'-phosphate, or 3-indolylpropanol 3'-phosphate. The structural basis for the reduced alpha-activity has its origins in the missing hydrogen bond between alphaThr183 and the catalytic residue, alphaAsp60.
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Affiliation(s)
- Victor Kulik
- Max Planck Institut für Molekulare Physiologie, Abeilung für Biophysikalische Chemie, Otto Hahn Str 11, 44227 Dortmund, Germany
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10
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Fehlner-Gardiner C, Roshick C, Carlson JH, Hughes S, Belland RJ, Caldwell HD, McClarty G. Molecular basis defining human Chlamydia trachomatis tissue tropism. A possible role for tryptophan synthase. J Biol Chem 2002; 277:26893-903. [PMID: 12011099 DOI: 10.1074/jbc.m203937200] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Here we report the cloning and sequencing of a region of the chlamydiae chromosome termed the "plasticity zone" from all the human serovars of C. trachomatis containing the tryptophan biosynthesis genes. Our results show that this region contains orthologues of the tryptophan repressor as well as the alpha and beta subunits of tryptophan synthase. Results from reverse transcription-PCR and Western blot analyses indicate that the trpBA genes are transcribed, and protein products are expressed. The TrpB sequences from all serovars are highly conserved. In comparison with other tryptophan synthase beta subunits, the chlamydial TrpB subunit retains all conserved amino acid residues required for beta reaction activity. In contrast, the chlamydial TrpA sequences display numerous mutations, which distinguish them from TrpA sequences of all other prokaryotes. All ocular serovars contain a deletion mutation resulting in a truncated TrpA protein, which lacks alpha reaction activity. The TrpA protein from the genital serovars retains conserved amino acids required for catalysis but has mutated several active site residues involved in substrate binding. Complementation analysis in Escherichia coli strains, with defined mutations in tryptophan biosynthesis, and in vitro enzyme activity data, with cloned TrpB and TrpA proteins, indicate these mutations result in a TrpA protein that is unable to utilize indole glycerol 3-phosphate as substrate. In contrast, the chlamydial TrpB protein can carry out the beta reaction, which catalyzes the formation of tryptophan from indole and serine. The activity of the chlamydial Trp B protein differs from that of the well characterized E. coli and Salmonella TrpBs in displaying an absolute requirement for full-length TrpA. Taken together our data indicate that genital, but not ocular, serovars are capable of utilizing exogenous indole for the biosynthesis of tryptophan.
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Affiliation(s)
- Christine Fehlner-Gardiner
- Department of Medical Microbiology, University of Manitoba and National Microbiology Laboratory, Health Canada, Winnipeg, Manitoba R3E 0W3, Canada
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11
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Weyand M, Schlichting I, Marabotti A, Mozzarelli A. Crystal structures of a new class of allosteric effectors complexed to tryptophan synthase. J Biol Chem 2002; 277:10647-52. [PMID: 11756456 DOI: 10.1074/jbc.m111285200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tryptophan synthase is a bifunctional alpha(2)beta(2) complex catalyzing the last two steps of l-tryptophan biosynthesis. The natural substrates of the alpha-subunit indole- 3-glycerolphosphate and glyceraldehyde-3-phosphate, and the substrate analogs indole-3-propanolphosphate and dl-alpha-glycerol-3-phosphate are allosteric effectors of the beta-subunit activity. It has been shown recently, that the indole-3-acetyl amino acids indole-3-acetylglycine and indole-3-acetyl-l-aspartic acid are both alpha-subunit inhibitors and beta-subunit allosteric effectors, whereas indole-3-acetyl-l-valine is only an alpha-subunit inhibitor (Marabotti, A., Cozzini, P., and Mozzarelli, A. (2000) Biochim. Biophys. Acta 1476, 287-299). The crystal structures of tryptophan synthase complexed with indole-3-acetylglycine and indole-3-acetyl-l-aspartic acid show that both ligands bind to the active site such that the carboxylate moiety is positioned similarly as the phosphate group of the natural substrates. As a consequence, the residues of the alpha-active site that interact with the ligands are the same as observed in the indole 3-glycerolphosphate-enzyme complex. Ligand binding leads to closure of loop alphaL6 of the alpha-subunit, a key structural element of intersubunit communication. This is in keeping with the allosteric role played by these compounds. The structure of the enzyme complex with indole-3-acetyl-l-valine is quite different. Due to the hydrophobic lateral chain, this molecule adopts a new orientation in the alpha-active site. In this case, closure of loop alphaL6 is no longer observed, in agreement with its functioning only as an inhibitor of the alpha-subunit reaction.
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Affiliation(s)
- Michael Weyand
- Max-Planck-Institut für Molekulare Physiologie, Abteilung für Physikalische Biochemie, D-44227 Dortmund, Germany
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12
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Marabotti A, Cozzini P, Mozzarelli A. Novel allosteric effectors of the tryptophan synthase alpha(2)beta(2) complex identified by computer-assisted molecular modeling. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1476:287-99. [PMID: 10669793 DOI: 10.1016/s0167-4838(99)00242-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Tryptophan synthase is a pyridoxal 5'-phosphate-dependent alpha(2)beta(2) complex catalyzing the formation of L-tryptophan. The functional properties of one subunit are allosterically regulated by ligands of the other subunit. Molecules tailored for binding to the alpha-active site were designed using as a starting model the three-dimensional structure of the complex between the enzyme from Salmonella typhimurium and the substrate analog indole-3-propanol phosphate. On the basis of molecular dynamics simulations, indole-3-acetyl-X, where X is glycine, alanine, valine and aspartate, and a few other structurally related compounds were found to be good candidates for ligands of the alpha-subunit. The binding of the designed compounds to the alpha-active site was evaluated by measuring the inhibition of the alpha-reaction of the enzyme from Salmonella typhimurium. The inhibition constants were found to vary between 0.3 and 1.7 mM. These alpha-subunit ligands do not bind to the beta-subunit, as indicated by the absence of effects on the rate of the beta-reaction in the isolated beta(2) dimer. A small inhibitory effect on the activity of the alpha(2)beta(2) complex was caused by indole-3-acetyl-glycine and indole-3-acetyl-aspartate whereas a small stimulatory effect was caused by indole-3-acetamide. Furthermore, indole-3-acetyl-glycine, indole-3-acetyl-aspartate and indole-3-acetamide perturb the equilibrium of the catalytic intermediates formed at the beta-active site, stabilizing the alpha-aminoacrylate Schiff base. These results indicate that (i) indole-3-acetyl-glycine, indole-3-acetyl-aspartate and indole-3-acetamide bind to the alpha-subunit and act as allosteric effectors whereas indole-3-acetyl-valine and indole-3-acetyl-alanine only bind to the alpha-subunit, and (ii) the terminal phosphate present in the already known allosteric effectors of tryptophan synthase is not strictly required for the transmission of regulatory signals.
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Affiliation(s)
- A Marabotti
- Institute of Biochemical Sciences, University of Parma, 43100, Parma, Italy
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13
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Streaker ED, Beckett D. Ligand-linked structural changes in the Escherichia coli biotin repressor: the significance of surface loops for binding and allostery. J Mol Biol 1999; 292:619-32. [PMID: 10497026 DOI: 10.1006/jmbi.1999.3086] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Escherichia coli repressor of biotin biosynthesis (BirA) is an allosteric site-specific DNA-binding protein. BirA catalyzes synthesis of biotinyl-5'-AMP from substrates biotin and ATP and the adenylate serves as the positive allosteric effector in binding of the repressor to the biotin operator sequence. Although a three-dimensional structure of the apo-repressor has been determined by X-ray crystallographic techniques, no structures of any ligand-bound forms of the repressor are yet available. Results of previously published solution studies are consistent with the occurrence of conformational changes in the protein concomitant with ligand binding. In this work the hydroxyl radical footprinting technique has been used to probe changes in reactivity of the peptide backbone of BirA that accompany ligand binding. Results of these studies indicate that binding of biotin to the protein results in protection of regions of the central domain in the vicinity of the active site and the C-terminal domain from chemical cleavage. Biotin-linked changes in reactivity constitute a subset of those linked to adenylate binding. Binding of both bio-5'-AMP and biotin operator DNA suppresses cleavage at additional sites in the amino and carboxy-terminal domains of the protein. Varying degrees of protection of the five surface loops on BirA from hydroxyl radical-mediated cleavage are observed in all complexes. These results implicate the C-terminal domain of BirA, for which no function has previously been known, in small ligand and site-specific DNA binding and highlight the significance of surface loops, some of which are disordered in the apoBirA structure, for ligand binding and transmission of allosteric information in the protein.
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Affiliation(s)
- E D Streaker
- Department of Chemistry, College of Life Sciences, University of Maryland,College Park, MD 20742-2021, USA
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14
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Woehl EU, Dunn MF. Monovalent metal ions play an essential role in catalysis and intersubunit communication in the tryptophan synthase bienzyme complex. Biochemistry 1995; 34:9466-76. [PMID: 7626617 DOI: 10.1021/bi00029a023] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
This investigation shows that the alpha 2 beta 2 tryptophan synthase bienzyme complex from Salmonella typhimurium is subject to monovalent metal ion activation. The effects of the monovalent metal ions Na+ and K+ were investigated using rapid scanning stopped-flow (RSSF), single-wavelength stopped-flow (SWSF), and steady-state techniques. RSSF measurements of individual steps in the reaction of L-serine and indole to give L-trytophan (the beta-reaction) as well as the reaction of 3-indole-D-glycerol 3'-phosphate (IGP) with L-serine (the alpha beta-reaction) demonstrate that monovalent metal ions such as Na+ and K+ change the distribution of intermediates in both the transient and steady states. Therefore the metal ion effect alters relative ground-state energies and the relative positions of ground- and transition-state energies. The RSSF spectra and SWSF time courses show that the turnover of indole is significantly reduced in the absence of either Na+ or K+. The alpha-aminoacrylate Schiff base species, E(A-A), is in a less active state in the absence of monovalent metal ions. Na+ decreases the steady-state rate of IGP cleavage (the alpha-reaction) to about 30% of the value obtained in the absence of metal ions. Steady-state investigations show that in the absence of monovalent metal ions the alpha- and alpha beta-reactions have the same activity. Na+ binding gives a 30-fold stimulation of the alpha-reaction when the beta-site is in the E(A-A) form.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- E U Woehl
- Department of Biochemistry, University of California at Riverside 92521-0129, USA
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15
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Ruvinov SB, Ahmed SA, McPhie P, Miles EW. Monovalent cations partially repair a conformational defect in a mutant tryptophan synthase alpha 2 beta 2 complex (beta-E109A). J Biol Chem 1995; 270:17333-8. [PMID: 7615535 DOI: 10.1074/jbc.270.29.17333] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We are using the tryptophan synthase alpha 2 beta 2 complex as a model system to investigate how ligands, protein-protein interaction, and mutations regulate enzyme activity, reaction specificity, and substrate specificity. The rate of conversion of L-serine and indole to L-tryptophan by the beta 2 subunit alone is quite low, but is activated by certain monovalent cations or by association with alpha subunit to form an alpha 2 beta 2 complex. Since monovalent cations and alpha subunit appear to stabilize an active conformation of the beta 2 subunit, we have investigated the effects of monovalent cations on the activities and spectroscopic properties of a mutant form of alpha 2 beta 2 complex having beta 2 subunit glutamic acid 109 replaced by alanine (E109A). The E109A alpha 2 beta 2 complex is inactive in reactions with L-serine but active in reactions with beta-chloro-L-alanine. Parallel experiments show effects of monovalent cations on the properties of wild type beta 2 subunit and alpha 2 beta 2 complex. We find that CsCl stimulates the activity of the E109A alpha 2 beta 2 complex and of wild type beta 2 subunit with L-serine and indole and alters the equilibrium distribution of L-serine reaction intermediates. The results indicate that CsCl partially repairs the deleterious effects of the E109A mutation on the activity of the alpha 2 beta 2 complex by stabilizing a conformation with catalytic properties more similar to those of the wild type alpha 2 beta 2 complex. This conclusion is consistent with observations that monovalent cations alter the catalytic and spectroscopic properties of several pyridoxal phosphate-dependent enzymes by stabilizing alternative conformations.
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Affiliation(s)
- S B Ruvinov
- Laboratory of Biochemical Pharmacology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0830, USA
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16
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Ruvinov SB, Yang XJ, Parris KD, Banik U, Ahmed SA, Miles EW, Sackett DL. Ligand-mediated changes in the tryptophan synthase indole tunnel probed by nile red fluorescence with wild type, mutant, and chemically modified enzymes. J Biol Chem 1995; 270:6357-69. [PMID: 7890774 DOI: 10.1074/jbc.270.11.6357] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The bacterial tryptophan synthase alpha 2 beta 2 complex contains an unusual structural feature: an intramolecular tunnel that channels indole from the active site of the alpha subunit to the active site of the beta subunit 25 A away. Here we investigate the role of the tunnel in communication between the alpha and beta subunits using the polarity-sensitive fluorescent probe, Nile Red. Interaction of Nile Red in the nonpolar tunnel near beta subunit residues Cys-170 and Phe-280 is supported by studies with enzymes altered at these positions. Restricting the tunnel by enlarging Cys-170 by chemical modification or mutagenesis decreases the fluorescence of Nile Red by 30-70%. Removal of a partial restriction in the tunnel by replacing Phe-280 by Cys or Ser increases the fluorescence of Nile Red more than 2-fold. A binding site for Nile Red in this region near the pyridoxal phosphate coenzyme of the beta subunit is further supported by iodide quenching and fluorescence energy transfer experiments and by molecular modeling based on the three-dimensional structure of the alpha 2 beta 2 complex. Finally, studies using Nile Red as a sensitive probe of conformational changes in the tunnel reveal that allosteric ligands (alpha subunit) or active site ligands (beta subunit) decrease the fluorescence of Nile Red. We speculate that allosteric and active site ligands induce a tunnel restriction near Phe-280 that serves as a gate to control passage of indole through the tunnel.
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Affiliation(s)
- S B Ruvinov
- Laboratory of Biochemical Pharmacology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892
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17
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Thermal inactivation of tryptophan synthase. Stabilization by protein-protein interaction and protein-ligand interaction. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32629-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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18
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Kempner ES. Movable lobes and flexible loops in proteins. Structural deformations that control biochemical activity. FEBS Lett 1993; 326:4-10. [PMID: 8325386 DOI: 10.1016/0014-5793(93)81749-p] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Two classes of protein whose structure is modified by small ligands are reviewed. Proteins of one group contain two massive domains joined by a flexible link; in response to small molecules, the two lobes approach and enclose the ligand. In the other, a short segment of amino acids moves as a flexible loop over the ligand which often is trapped in a non-aqueous environment. Biochemical reaction rates are altered dramatically by these movements.
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Affiliation(s)
- E S Kempner
- Laboratory of Physical Biology National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892
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Strambini GB, Cioni P, Peracchi A, Mozzarelli A. Conformational changes and subunit communication in tryptophan synthase: effect of substrates and substrate analogs. Biochemistry 1992; 31:7535-42. [PMID: 1510940 DOI: 10.1021/bi00148a014] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The transmission of regulatory signals between the alpha- and beta-subunits of the tryptophan synthase alpha 2 beta 2 complex from Salmonella typhimurium has been investigated by monitoring the luminescence properties of the enzyme in the presence and in the absence of the alpha-subunit ligand DL-alpha-glycerol 3-phosphate, the alpha- and beta-subunit substrate indole, and the beta-subunit substrate analog L-histidine. The beta-subunit contains as intrinsic probes Trp-177 and pyridoxal 5'-phosphate, whereas the alpha-subunit has been mutagenized by replacing Ala-129 with a Trp residue. In contrast to the inertness of L-histidine, DL-alpha-glycerol 3-phosphate was found (i) to alter the phosphorescence spectrum of Trp-129, (ii) to shift the fluorescence thermal quenching profile of both Trp-177 and coenzyme to higher temperature, (iii) to slow down the triplet decay kinetics of Trp-177 in fluid solution, and (iv) to affect the equilibrium between different conformations of the enzyme. These findings provide direct evidence that DL-alpha-glycerol 3-phosphate binding affects the structure of the alpha-subunit and, in the presence of coenzyme, induces a conformational change in the beta-subunit that leads to a considerably more rigid structure. As opposed to DL-alpha-glycerol 3-phosphate, the shortening of the phosphorescence lifetime upon indole binding suggests that this substrate increases structural fluctuations in the beta-subunit. Implications for the mechanism of the allosteric regulation between alpha- and beta-subunits are discussed.
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Brzović P, Sawa Y, Hyde C, Miles E, Dunn M. Evidence that mutations in a loop region of the alpha-subunit inhibit the transition from an open to a closed conformation in the tryptophan synthase bienzyme complex. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42377-0] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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21
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Threonine 183 and adjacent flexible loop residues in the tryptophan synthase alpha subunit have critical roles in modulating the enzymatic activities of the beta subunit in the alpha 2 beta 2 complex. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42548-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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22
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Ruvinov SB, Miles EW. Subunit communication in the tryptophan synthase alpha 2 beta 2 complex. Effects of beta subunit ligands on proteolytic cleavage of a flexible loop in the alpha subunit. FEBS Lett 1992; 299:197-200. [PMID: 1544494 DOI: 10.1016/0014-5793(92)80246-d] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
To probe the structural basis for ligand-mediated communication between the alpha and beta subunits in the tryptophan synthase alpha 2 beta 2 complex, we have determined the effects of ligands of the alpha and beta subunits on proteolysis of a flexible loop in the alpha subunit. We find that addition of a ligand of the beta subunit (L-serine, D-tryptophan, or L-tryptophan) in combination with a ligand of the alpha subunit (alpha-glycerol 3-phosphate) almost completely prevents the tryptic cleavage of the alpha subunit loop. Thus, the binding of a ligand to the beta-site affects the conformation of the alpha subunit 25-30 A distant.
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Affiliation(s)
- S B Ruvinov
- Laboratory of Biochemical Pharmacology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
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