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Streit JO, Bukvin IV, Chan SHS, Bashir S, Woodburn LF, Włodarski T, Figueiredo AM, Jurkeviciute G, Sidhu HK, Hornby CR, Waudby CA, Cabrita LD, Cassaignau AME, Christodoulou J. The ribosome lowers the entropic penalty of protein folding. Nature 2024; 633:232-239. [PMID: 39112704 PMCID: PMC11374706 DOI: 10.1038/s41586-024-07784-4] [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: 08/10/2023] [Accepted: 07/04/2024] [Indexed: 08/17/2024]
Abstract
Most proteins fold during biosynthesis on the ribosome1, and co-translational folding energetics, pathways and outcomes of many proteins have been found to differ considerably from those in refolding studies2-10. The origin of this folding modulation by the ribosome has remained unknown. Here we have determined atomistic structures of the unfolded state of a model protein on and off the ribosome, which reveal that the ribosome structurally expands the unfolded nascent chain and increases its solvation, resulting in its entropic destabilization relative to the peptide chain in isolation. Quantitative 19F NMR experiments confirm that this destabilization reduces the entropic penalty of folding by up to 30 kcal mol-1 and promotes formation of partially folded intermediates on the ribosome, an observation that extends to other protein domains and is obligate for some proteins to acquire their active conformation. The thermodynamic effects also contribute to the ribosome protecting the nascent chain from mutation-induced unfolding, which suggests a crucial role of the ribosome in supporting protein evolution. By correlating nascent chain structure and dynamics to their folding energetics and post-translational outcomes, our findings establish the physical basis of the distinct thermodynamics of co-translational protein folding.
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Affiliation(s)
- Julian O Streit
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Ivana V Bukvin
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Sammy H S Chan
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK.
| | - Shahzad Bashir
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Lauren F Woodburn
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Tomasz Włodarski
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Angelo Miguel Figueiredo
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Gabija Jurkeviciute
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Haneesh K Sidhu
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Charity R Hornby
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Christopher A Waudby
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Lisa D Cabrita
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK
| | - Anaïs M E Cassaignau
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK.
| | - John Christodoulou
- Institute of Structural and Molecular Biology, Department of Structural and Molecular Biology, University College London, London, UK.
- Department of Biological Sciences, Birkbeck College, London, UK.
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2
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Hidalgo F, Nocka LM, Shah NH, Gorday K, Latorraca NR, Bandaru P, Templeton S, Lee D, Karandur D, Pelton JG, Marqusee S, Wemmer D, Kuriyan J. A saturation-mutagenesis analysis of the interplay between stability and activation in Ras. eLife 2022; 11:e76595. [PMID: 35272765 PMCID: PMC8916776 DOI: 10.7554/elife.76595] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Accepted: 01/25/2022] [Indexed: 12/31/2022] Open
Abstract
Cancer mutations in Ras occur predominantly at three hotspots: Gly 12, Gly 13, and Gln 61. Previously, we reported that deep mutagenesis of H-Ras using a bacterial assay identified many other activating mutations (Bandaru et al., 2017). We now show that the results of saturation mutagenesis of H-Ras in mammalian Ba/F3 cells correlate well with the results of bacterial experiments in which H-Ras or K-Ras are co-expressed with a GTPase-activating protein (GAP). The prominent cancer hotspots are not dominant in the Ba/F3 data. We used the bacterial system to mutagenize Ras constructs of different stabilities and discovered a feature that distinguishes the cancer hotspots. While mutations at the cancer hotspots activate Ras regardless of construct stability, mutations at lower-frequency sites (e.g. at Val 14 or Asp 119) can be activating or deleterious, depending on the stability of the Ras construct. We characterized the dynamics of three non-hotspot activating Ras mutants by using NMR to monitor hydrogen-deuterium exchange (HDX). These mutations result in global increases in HDX rates, consistent with destabilization of Ras. An explanation for these observations is that mutations that destabilize Ras increase nucleotide dissociation rates, enabling activation by spontaneous nucleotide exchange. A further stability decrease can lead to insufficient levels of folded Ras - and subsequent loss of function. In contrast, the cancer hotspot mutations are mechanism-based activators of Ras that interfere directly with the action of GAPs. Our results demonstrate the importance of GAP surveillance and protein stability in determining the sensitivity of Ras to mutational activation.
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Affiliation(s)
- Frank Hidalgo
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Howard Hughes Medical Institute, University of California, BerkeleyBerkeleyUnited States
- Department of Chemistry, University of California, BerkeleyBerkeleyUnited States
| | - Laura M Nocka
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Howard Hughes Medical Institute, University of California, BerkeleyBerkeleyUnited States
- Department of Chemistry, University of California, BerkeleyBerkeleyUnited States
| | - Neel H Shah
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Howard Hughes Medical Institute, University of California, BerkeleyBerkeleyUnited States
- Department of Molecular and Cell Biology, University of California, BerkeleyBerkeleyUnited States
- Department of Chemistry, Columbia UniversityNew YorkUnited States
| | - Kent Gorday
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Howard Hughes Medical Institute, University of California, BerkeleyBerkeleyUnited States
- Biophysics Graduate Group, University of California, BerkeleyBerkeleyUnited States
| | - Naomi R Latorraca
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Department of Molecular and Cell Biology, University of California, BerkeleyBerkeleyUnited States
| | - Pradeep Bandaru
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Howard Hughes Medical Institute, University of California, BerkeleyBerkeleyUnited States
- Department of Molecular and Cell Biology, University of California, BerkeleyBerkeleyUnited States
| | - Sage Templeton
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Howard Hughes Medical Institute, University of California, BerkeleyBerkeleyUnited States
| | - David Lee
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Howard Hughes Medical Institute, University of California, BerkeleyBerkeleyUnited States
| | - Deepti Karandur
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Howard Hughes Medical Institute, University of California, BerkeleyBerkeleyUnited States
- Department of Molecular and Cell Biology, University of California, BerkeleyBerkeleyUnited States
| | - Jeffrey G Pelton
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
| | - Susan Marqusee
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Department of Chemistry, University of California, BerkeleyBerkeleyUnited States
- Department of Molecular and Cell Biology, University of California, BerkeleyBerkeleyUnited States
| | - David Wemmer
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Department of Chemistry, University of California, BerkeleyBerkeleyUnited States
| | - John Kuriyan
- California Institute for Quantitative Biosciences (QB3), University of California, BerkeleyBerkeleyUnited States
- Howard Hughes Medical Institute, University of California, BerkeleyBerkeleyUnited States
- Department of Chemistry, University of California, BerkeleyBerkeleyUnited States
- Department of Molecular and Cell Biology, University of California, BerkeleyBerkeleyUnited States
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3
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Toyama Y, Kontani K, Katada T, Shimada I. Decreased conformational stability in the oncogenic N92I mutant of Ras-related C3 botulinum toxin substrate 1. SCIENCE ADVANCES 2019; 5:eaax1595. [PMID: 31457101 PMCID: PMC6685717 DOI: 10.1126/sciadv.aax1595] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Accepted: 06/27/2019] [Indexed: 06/10/2023]
Abstract
Ras-related C3 botulinum toxin substrate 1 (Rac1) functions as a molecular switch by cycling between an inactive guanosine diphosphate (GDP)-bound state and an active guanosine triphosphate (GTP)-bound state. An oncogenic mutant of Rac1, an N92I mutant, strongly promotes cell proliferation and subsequent oncogenic activities by facilitating the intrinsic GDP dissociation in the inactive GDP-bound state. Here, we used solution nuclear magnetic resonance spectroscopy to investigate the activation mechanism of the N92I mutant. We found that the static structure of the GDP binding site is not markedly perturbed by the mutation, but the overall conformational stability decreases in the N92I mutant, which then facilitates GDP dissociation by lowering the activation energy for the dissociation reaction. On the basis of these results, we proposed the activation mechanism of the N92I mutant, in which the decreased conformational stability plays important roles in its activation process.
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Affiliation(s)
- Yuki Toyama
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
- Japan Biological Informatics Consortium (JBiC), Aomi, Koto-ku, Tokyo 135-0064, Japan
| | - Kenji Kontani
- Department of Biochemistry, Meiji Pharmaceutical University, Kiyose, Tokyo 204-8588, Japan
| | - Toshiaki Katada
- Molecular Cell Biology Laboratory, Research Institute of Pharmaceutical Sciences, Faculty of Pharmacy, Musashino University, Tokyo 202-8585, Japan
| | - Ichio Shimada
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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4
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Maheshwari D, Yadav R, Rastogi R, Jain A, Tripathi S, Mukhopadhyay A, Arora A. Structural and Biophysical Characterization of Rab5a from Leishmania Donovani. Biophys J 2018; 115:1217-1230. [PMID: 30241678 PMCID: PMC6170798 DOI: 10.1016/j.bpj.2018.08.032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Revised: 08/10/2018] [Accepted: 08/15/2018] [Indexed: 12/21/2022] Open
Abstract
Leishmania donovani possess two isoforms of Rab5 (Rab5a and Rab5b), which are involved in fluid phase and receptor-mediated endocytosis, respectively. We have characterized the solution structure and dynamics of a stabilized truncated LdRab5a mutant. For the purpose of NMR structure determination, protein stability was enhanced by systematically introducing various deletions and mutations. Deletion of hypervariable C-terminal and the 20 residues LdRab5a specific insert slightly enhanced the stability, which was further improved by C107S mutation. The final construct, truncated LdRab5a with C107S mutation, was found to be stable for longer durations at higher concentration, with an increase in melting temperature by 10°C. Solution structure of truncated LdRab5a shows the characteristic GTPase fold having nucleotide and effector binding sites. Orientation of switch I and switch II regions match well with that of guanosine 5'-(β, γ-imido)triphosphate (GppNHp)-bound human Rab5a, indicating that the truncated LdRab5a attains the canonical GTP bound state. However, the backbone dynamics of the P-loop, switch I, and switch II regions were slower than that observed for guanosine 5'-(β, γ-imido)triphosphate (GMPPNP)-bound H-Ras. This dynamic profile may further complement the residue-specific complementarity in determining the specificity of interaction with the effectors. In parallel, biophysical investigations revealed the urea induced unfolding of truncated LdRab5a to be a four-state process that involved two intermediates, I1 and I2. The maximal 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid (Bis-ANS) binding was observed for I2 state, which was inferred to have molten globule like characteristics. Overall, the strategy presented would have significant impact for studying other Rab and small GTPase proteins by NMR spectroscopy.
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Affiliation(s)
- Diva Maheshwari
- Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow, India
| | - Rahul Yadav
- Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow, India
| | - Ruchir Rastogi
- Cell Biology Lab, National Institute of Immunology, New Delhi, India
| | - Anupam Jain
- Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow, India
| | - Sarita Tripathi
- Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow, India
| | | | - Ashish Arora
- Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow, India.
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5
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Martikkala E, Veltel S, Kirjavainen J, Rozwandowicz-Jansen A, Lamminmäki U, Hänninen P, Härmä H. Homogeneous single-label biochemical Ras activation assay using time-resolved luminescence. Anal Chem 2011; 83:9230-3. [PMID: 22098697 DOI: 10.1021/ac202723h] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Mutations of the small GTP-binding protein Ras have been commonly found in tumors, and Ras oncogenes have been established to be involved in the early steps of cancerogenesis. The detection of Ras activity is critical in the determination of the cell signaling events controlling cell growth and differentiation. Therefore, development of improved methods for primary screening of novel potential drugs that target small GTPase or their regulators and their signaling pathways is important. Several assays have been developed for small GTPases studies, but all these methods have limitations for a high-throughput screening (HTS) use. Multiple steps including separation, use of radioactive labels or time-consuming immunoblotting, and a need of large quantities of purified proteins are decreasing the user-friendliness of these methods. Here, we have developed a homogeneous H-Ras activity assay based on a single-label utilizing the homogeneous quenching resonance energy transfer technique (QRET). In the QRET method, the binding of a terbium-labeled GTP (Tb-GTP) to small GTPase protein H-Ras protects the signal of the label from quenching, whereas the signal of the nonbound fraction of Tb-GTP is quenched by a soluble quencher. This enables a rapid determination of the changes in the activity status of Ras. The assay optimization showed that only 60 nM concentration of purified H-Ras protein was needed. The functionality of the assay was proved by detecting the effect of H-Ras guanine nucleotide exchange factor, Son of Sevenless. The signal-to-background ratio up to 7.7 was achieved with an average assay coefficient of variation of 9.1%. The use of a low concentration of purified protein is desirable and the signal-to-background ratio of 3.4 was achieved in the assay at a concentration of 60 nM for H-Ras and SOS proteins. The need of only one labeled molecule and the ability to decrease the quantities of purified proteins used in the experiments are valuable qualities in HTS showing the potential of the QRET method.
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6
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The removal of a disulfide bridge in CotA-laccase changes the slower motion dynamics involved in copper binding but has no effect on the thermodynamic stability. J Biol Inorg Chem 2011; 16:641-51. [DOI: 10.1007/s00775-011-0768-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Accepted: 02/08/2011] [Indexed: 10/18/2022]
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7
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Abstract
Purines are critical cofactors in the enzymatic reactions that create and maintain living organisms. In humans, there are approximately 3,266 proteins that utilize purine cofactors and these proteins constitute the so-called purinome. The human purinome encompasses a wide-ranging functional repertoire and many of these proteins are attractive drug targets. For example, it is estimated that 30% of modern drug discovery projects target protein kinases and that modulators of small G-proteins comprise more than 50% of currently marketed drugs. Given the importance of purine-binding proteins to drug discovery, the following review will discuss the forces that mediate protein:purine recognition, the factors that determine druggability of a protein target, and the process of structure-based drug design. A review of purine recognition in representatives of the various purine-binding protein families, as well as the challenges faced in targeting members of the purinome in drug discovery campaigns will also be given.
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Affiliation(s)
- Jeremy M Murray
- Department of Protein Engineering, Genentech, Inc., South San Francisco, CA, USA
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8
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Itzen A, Pylypenko O, Goody RS, Alexandrov K, Rak A. Nucleotide exchange via local protein unfolding--structure of Rab8 in complex with MSS4. EMBO J 2006; 25:1445-55. [PMID: 16541104 PMCID: PMC1440319 DOI: 10.1038/sj.emboj.7601044] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2005] [Accepted: 02/20/2006] [Indexed: 11/08/2022] Open
Abstract
Rab GTPases function as essential regulators of vesicle transport in eukaryotic cells. MSS4 was shown to stimulate nucleotide exchange on Rab proteins associated with the exocytic pathway and to have nucleotide-free-Rab chaperone activity. A detailed kinetic analysis of MSS4 interaction with Rab8 showed that MSS4 is a relatively slow exchange factor that forms a long-lived nucleotide-free complex with RabGTPase. In contrast to other characterized exchange factor-GTPase complexes, MSS4:Rab8 complex binds GTP faster than GDP, but still ca. 3 orders of magnitude more slowly than comparable complexes. The crystal structure of the nucleotide-free MSS4:Rab8 complex revealed that MSS4 binds to the Switch I and interswitch regions of Rab8, forming an intermolecular beta-sheet. Complex formation results in dramatic structural changes of the Rab8 molecule, leading to unfolding of the nucleotide-binding site and surrounding structural elements, facilitating nucleotide release and slowing its rebinding. Coupling of nucleotide exchange activity to a cycle of GTPase unfolding and refolding represents a novel nucleotide exchange mechanism.
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Affiliation(s)
- Aymelt Itzen
- Max-Planck-Institute for Molecular Physiology, Dortmund, Germany
| | - Olena Pylypenko
- Max-Planck-Institute for Molecular Physiology, Dortmund, Germany
| | - Roger S Goody
- Max-Planck-Institute for Molecular Physiology, Dortmund, Germany
| | | | - Alexey Rak
- Max-Planck-Institute for Molecular Physiology, Dortmund, Germany
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9
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Schubert P, Pfleiderer K, Hillen W. Tet repressor residues indirectly recognizing anhydrotetracycline. ACTA ACUST UNITED AC 2004; 271:2144-52. [PMID: 15153105 DOI: 10.1111/j.1432-1033.2004.04130.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Two tetracycline repressor (TetR) sequence variants sharing 63% identical amino acids were investigated in terms of their recognition specificity for tetracycline and anhydrotetracycline. Thermodynamic complex stabilities determined by urea-dependent unfolding reveal that tetracycline stabilizes both variants to a similar extent but that anhydrotetracycline discriminates between them significantly. Isofunctional TetR hybrid proteins of these sequence variants were constructed and their denaturation profiles identified residues 57 and 61 as the complex stability determinant. Association kinetics reveal different recognition of these TetR variants by anhydrotetracycline, but the binding constants indicate similar stabilization. The identified residues connect to an internal water network, which suggests that the discrepancy in the observed thermodynamics may be caused by an entropy effect. Exchange of these interacting residues between the two TetR variants appears to influence the flexibility of this water organization, demonstrating the importance of buried, structural water molecules for ligand recognition and protein function. Therefore, this structural module seems to be a key requisite for the plasticity of the multiple ligand binding protein TetR.
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Affiliation(s)
- Peter Schubert
- Lehrstuhl für Mikrobiologie, Institut für Mikrobiologie, Biochemie und Genetik, Friedrich-Alexander-Universität Erlangen-Nurnberg, Staudtstrasse 5, 91058 Erlangen, Germany
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10
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Becker CFW, Hunter CL, Seidel R, Kent SBH, Goody RS, Engelhard M. Total chemical synthesis of a functional interacting protein pair: the protooncogene H-Ras and the Ras-binding domain of its effector c-Raf1. Proc Natl Acad Sci U S A 2003; 100:5075-80. [PMID: 12704243 PMCID: PMC154300 DOI: 10.1073/pnas.0831227100] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Generation of biological function by chemical methods is potentially of great importance for the understanding and targeting of physiological processes. Chemical synthesis of proteins offers the ability to alter the properties of target protein molecules in a tailor-made fashion. In the present work it is demonstrated that this methodology can be expanded to the elucidation of protein-protein interactions as exemplified by the complete chemical synthesis of the protooncogene product H-Ras as well as of the Ras-binding domain (RBD) of its effector c-Raf1. The 166-aa polypeptide chain of H-Ras was synthesized by native chemical ligation of three unprotected peptide segments. Similarly, the 81-aa RBD was prepared by ligation of two peptide segments. Both RBD and Ras displayed functional and spectroscopic properties indistinguishable from their recombinant forms as judged by CD spectroscopy and from transient kinetic measurements of the Ras-RBD interaction as well as from nucleotide replacement reactions in Ras. An unnatural amino acid bearing a nitrobenzofurazan side chain was introduced into position 91 of the RBD, providing unique fluorescence properties. The association transient of nitrobenzofurazan labeled with Ras.guanosine 5'-beta,gamma-imidotriphosphate showed a slow phase that had not been detected in earlier work by using other signals.
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Affiliation(s)
- Christian F W Becker
- Max-Planck-Institut für Molekulare Physiologie, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany
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11
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Wallace LA, Matthews CR. Sequential vs. parallel protein-folding mechanisms: experimental tests for complex folding reactions. Biophys Chem 2002; 101-102:113-31. [PMID: 12487994 DOI: 10.1016/s0301-4622(02)00155-2] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The recent emphasis on rough energy landscapes for protein folding reactions by theoreticians, and the many observations of complex folding kinetics by experimentalists provide a rationale for a brief literature survey of various empirical approaches for validating the underlying mechanisms. The determination of the folding mechanism is a key step in defining the energy surface on which the folding reactions occurs and in interpreting the effects of amino acid replacements on this reaction. Case studies that illustrate methods for differentiating between sequential and parallel channel folding mechanisms are presented. The ultimate goal of such efforts is to understand how the one-dimensional information contained in the amino acid sequence is rapidly and efficiently translated into three-dimensional structure.
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Affiliation(s)
- Louise A Wallace
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA
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12
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Cerasoli E, Kelly SM, Coggins JR, Boam DJ, Clarke DT, Price NC. The refolding of type II shikimate kinase from Erwinia chrysanthemi after denaturation in urea. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:2124-32. [PMID: 11985590 DOI: 10.1046/j.1432-1033.2002.ejb.02862.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Shikimate kinase was chosen as a convenient representative example of the subclass of alpha/beta proteins with which to examine the mechanism of protein folding. In this paper we report on the refolding of the enzyme after denaturation in urea. As shown by the changes in secondary and tertiary structure monitored by far UV circular dichroism (CD) and fluorescence, respectively, the enzyme was fully unfolded in 4 m urea. From an analysis of the unfolding curve in terms of the two-state model, the stability of the folded state could be estimated as 17 kJ.mol-1. Approximately 95% of the enzyme activity could be recovered on dilution of the urea from 4 to 0.36 m. The results of spectroscopic studies indicated that refolding occurred in at least four kinetic phases, the slowest of which (k = 0.009 s-1) corresponded with the regain of shikimate binding and of enzyme activity. The two most rapid phases were associated with a substantial increase in the binding of 8-anilino-1-naphthalenesulfonic acid with only modest changes in the far UV CD, indicating that a collapsed intermediate with only partial native secondary structure was formed rapidly. The relevance of the results to the folding of other alpha/beta domain proteins is discussed.
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Affiliation(s)
- Eleonora Cerasoli
- Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, Joseph Black Building, University of Glasgow, Scotland, UK
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13
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Wallace LA, Robert Matthews C. Highly divergent dihydrofolate reductases conserve complex folding mechanisms. J Mol Biol 2002; 315:193-211. [PMID: 11779239 DOI: 10.1006/jmbi.2001.5230] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To test the hypothesis that protein folding mechanisms are better conserved than amino acid sequences, the mechanisms for dihydrofolate reductases (DHFR) from human (hs), Escherichia coli (ec) and Lactobacillus casei (lc) were elucidated and compared using intrinsic Trp fluorescence and fluorescence-detected 8-anilino-1-naphthalenesulfonate (ANS) binding. The development of the native state was monitored using either methotrexate (absorbance at 380 nm) or NADPH (extrinsic fluorescence) binding. All three homologs displayed complex unfolding and refolding kinetic mechanisms that involved partially folded states and multiple energy barriers. Although the pairwise sequence identities are less than 30 %, folding to the native state occurs via parallel folding channels and involves two types of on-pathway kinetic intermediates for all three homologs. The first ensemble of kinetic intermediates, detected within a few milliseconds, has significant secondary structure and exposed hydrophobic cores. The second ensemble is obligatory and has native-like side-chain packing in a hydrophobic core; however, these intermediates are unable to bind active-site ligands. The formation of the ensemble of native states occurs via three channels for hsDHFR, and four channels for lcDHFR and ecDHFR. The binding of active-site ligands (methotrexate and NADPH) accompanies the rate-limiting formation of the native ensemble. The conservation of the fast, intermediate and slow-folding events for this complex alpha/beta motif provides convincing evidence for the hypothesis that evolutionarily related proteins achieve the same fold via similar pathways.
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Affiliation(s)
- Louise A Wallace
- Department of Chemistry and Center for Biomolecular Structure and Function, The Pennsylvania State University, PA 16802, USA
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14
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Cheng H, Sukal S, Callender R, Leyh TS. gamma-phosphate protonation and pH-dependent unfolding of the Ras.GTP.Mg2+ complex: a vibrational spectroscopy study. J Biol Chem 2001; 276:9931-5. [PMID: 11124953 DOI: 10.1074/jbc.m009295200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The interdependence of GTP hydrolysis and the second messenger functions of virtually all GTPases has stimulated intensive study of the chemical mechanism of the hydrolysis. Despite numerous mutagenesis studies, the presumed general base, whose role is to activate hydrolysis by abstracting a proton from the nucleophilic water, has not been identified. Recent theoretical and experimental work suggest that the gamma-phosphate of GTP could be the general base. The current study investigates this possibility by studying the pH dependence of the vibrational spectrum of the Ras.GTP.Mg(2+) and Ras.GDP.Mg(2+) complexes. Isotope-edited IR studies of the Ras.GTP.Mg(2+) complex show that GTP remains bound to Ras at pH as low as 2.0 and that the gamma-phosphate is not protonated at pH > or = 3.3, indicating that the active site decreases the gamma-phosphate pK(a) by at least 1.1 pK(a) units compared with solution. Amide I studies show that the Ras.GTP.Mg(2+) and Ras.GDP.Mg(2+) complexes partially unfold in what appear to be two transitions. The first occurs in the pH range 5.4-2.6 and is readily reversible. Differences in the pH-unfolding midpoints for the Ras.GTP.Mg(2+) and Ras.GDP.Mg(2+) complexes (3.7 and 4.8, respectively) reveal that the enzyme-gamma-phosphoryl interactions stabilize the structure. The second transition, pH 2.6-1.7, is not readily reversed. The pH-dependent unfolding of the Ras.GTP.Mg(2+) complex provides an alternative interpretation of the data that had been used to support the gamma-phosphate mechanism, thereby raising the issue of whether this mechanism is operative in GTPase-catalyzed GTP hydrolysis reactions.
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Affiliation(s)
- H Cheng
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461-1926, USA
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Abstract
Several methods for determination of the secondary structure of proteins by spectroscopic measurements are reviewed. Circular dichroism (CD) spectroscopy provides rapid determinations of protein secondary structure with dilute solutions and a way to rapidly assess conformational changes resulting from addition of ligands. Both CD and Raman spectroscopies are particularly useful for measurements over a range of temperatures. Infrared (IR) and Raman spectroscopy require only small volumes of protein solution. The frequencies of amide bands are analyzed to determine the distribution of secondary structures in proteins. NMR chemical shifts may also be used to determine the positions of secondary structure within the primary sequence of a protein. However, the chemical shifts must first be assigned to particular residues, making the technique considerably slower than the optical methods. These data, together with sophisticated molecular modeling techniques, allow for refinement of protein structural models as well as rapid assessment of conformational changes resulting from ligand binding or macromolecular interactions. A selected number of examples are given to illustrate the power of the techniques in applications of biological interest.
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Affiliation(s)
- J T Pelton
- Hoechst Marion Roussel, Route 202-206, Bridgewater, New Jersey 08807-0800, USA.
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