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Behlendorf C, Diwo M, Neumann-Schaal M, Fuchs M, Körner D, Jänsch L, Faber F, Blankenfeldt W. Formation of the pyruvoyl-dependent proline reductase Prd from Clostridioides difficile requires the maturation enzyme PrdH. PNAS NEXUS 2024; 3:pgae249. [PMID: 38979079 PMCID: PMC11229817 DOI: 10.1093/pnasnexus/pgae249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Accepted: 06/09/2024] [Indexed: 07/10/2024]
Abstract
Stickland fermentation, the coupled oxidation and reduction of amino acid pairs, is a major pathway for obtaining energy in the nosocomial bacterium Clostridioides difficile. D-proline is the preferred substrate for the reductive path, making it not only a key component of the general metabolism but also impacting on the expression of the clostridial toxins TcdA and TcdB. D-proline reduction is catalyzed by the proline reductase Prd, which belongs to the pyruvoyl-dependent enzymes. These enzymes are translated as inactive proenzymes and require subsequent processing to install the covalently bound pyruvate. Whereas pyruvoyl formation by intramolecular serinolysis has been studied in unrelated enzymes, details about pyruvoyl generation by cysteinolysis as in Prd are lacking. Here, we show that Prd maturation requires a small dimeric protein that we have named PrdH. PrdH (CD630_32430) is co-encoded with the PrdA and PrdB subunits of Prd and also found in species producing similar reductases. By producing stable variants of PrdA and PrdB, we demonstrate that PrdH-mediated cleavage and pyruvoyl formation in the PrdA subunit requires PrdB, which can be harnessed to produce active recombinant Prd for subsequent analyses. We further created PrdA- and PrdH-mutants to get insight into the interaction of the components and into the processing reaction itself. Finally, we show that deletion of prdH renders C. difficile insensitive to proline concentrations in culture media, suggesting that this processing factor is essential for proline utilization. Due to the link between Stickland fermentation and pathogenesis, we suggest PrdH may be an attractive target for drug development.
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Affiliation(s)
- Christian Behlendorf
- Department Structure and Function of Proteins, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany
| | - Maurice Diwo
- Department Structure and Function of Proteins, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany
| | - Meina Neumann-Schaal
- Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, 38124 Braunschweig, Germany
- Institute for Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, 38106 Braunschweig, Germany
| | - Manuela Fuchs
- Helmholtz Centre for Infection Research (HZI), Helmholtz Institute for RNA-based Infection Research (HIRI), 97080 Würzburg, Germany
- Faculty of Medicine, Institute for Molecular Infection Biology (IMIB), Julius-Maximilians-University of Würzburg (JMU), 97080 Würzburg, Germany
| | - Dominik Körner
- Cellular Proteomics, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany
| | - Lothar Jänsch
- Cellular Proteomics, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany
| | - Franziska Faber
- Helmholtz Centre for Infection Research (HZI), Helmholtz Institute for RNA-based Infection Research (HIRI), 97080 Würzburg, Germany
- Faculty of Medicine, Institute for Molecular Infection Biology (IMIB), Julius-Maximilians-University of Würzburg (JMU), 97080 Würzburg, Germany
| | - Wulf Blankenfeldt
- Department Structure and Function of Proteins, Helmholtz Centre for Infection Research, 38124 Braunschweig, Germany
- Institute for Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, 38106 Braunschweig, Germany
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Evans R, Krahn N, Weiss J, Vincent KA, Söll D, Armstrong FA. Replacing a Cysteine Ligand by Selenocysteine in a [NiFe]-Hydrogenase Unlocks Hydrogen Production Activity and Addresses the Role of Concerted Proton-Coupled Electron Transfer in Electrocatalytic Reversibility. J Am Chem Soc 2024; 146:16971-16976. [PMID: 38747098 PMCID: PMC11212049 DOI: 10.1021/jacs.4c03489] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Revised: 05/09/2024] [Accepted: 05/10/2024] [Indexed: 06/27/2024]
Abstract
Hydrogenases catalyze hydrogen/proton interconversion that is normally electrochemically reversible (having minimal overpotential requirement), a special property otherwise almost exclusive to platinum metals. The mechanism of [NiFe]-hydrogenases includes a long-range proton-coupled electron-transfer process involving a specific Ni-coordinated cysteine and the carboxylate of a nearby glutamate. A variant in which this cysteine has been exchanged for selenocysteine displays two distinct changes in electrocatalytic properties, as determined by protein film voltammetry. First, proton reduction, even in the presence of H2 (a strong product inhibitor), is greatly enhanced relative to H2 oxidation: this result parallels a characteristic of natural [NiFeSe]-hydrogenases which are superior H2 production catalysts. Second, an inflection (an S-shaped "twist" in the trace) appears around the formal potential, the small overpotentials introduced in each direction (oxidation and reduction) signaling a departure from electrocatalytic reversibility. Concerted proton-electron transfer offers a lower energy pathway compared to stepwise transfers. Given the much lower proton affinity of Se compared to that of S, the inflection provides compelling evidence that concerted proton-electron transfer is important in determining why [NiFe]-hydrogenases are reversible electrocatalysts.
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Affiliation(s)
- Rhiannon
M. Evans
- Department
of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Natalie Krahn
- Department
of Biochemistry and Molecular Biology, University
of Georgia, Athens, Georgia 30602, United
States
| | - Joshua Weiss
- Department
of Biochemistry and Molecular Biology, University
of Georgia, Athens, Georgia 30602, United
States
| | - Kylie A. Vincent
- Department
of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Dieter Söll
- Department
of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06511, United States
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Fraser A. Armstrong
- Department
of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
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3
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Bennett ZD, Brunold TC. Non-standard amino acid incorporation into thiol dioxygenases. Methods Enzymol 2024; 703:121-145. [PMID: 39260993 PMCID: PMC11391102 DOI: 10.1016/bs.mie.2024.05.022] [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] [Indexed: 09/13/2024]
Abstract
Thiol dioxygenases (TDOs) are non‑heme Fe(II)‑dependent enzymes that catalyze the O2-dependent oxidation of thiol substrates to their corresponding sulfinic acids. Six classes of TDOs have thus far been identified and two, cysteine dioxygenase (CDO) and cysteamine dioxygenase (ADO), are found in eukaryotes. All TDOs belong to the cupin superfamily of enzymes, which share a common β‑barrel fold and two cupin motifs: G(X)5HXH(X)3-6E(X)6G and G(X)5-7PXG(X)2H(X)3N. Crystal structures of TDOs revealed that these enzymes contain a relatively rare, neutral 3‑His iron‑binding facial triad. Despite this shared metal-binding site, TDOs vary greatly in their secondary coordination spheres. Site‑directed mutagenesis has been used extensively to explore the impact of changes in secondary sphere residues on substrate specificity and enzymatic efficiency. This chapter summarizes site-directed mutagenesis studies of eukaryotic TDOs, focusing on the tools and practicality of non‑standard amino acid incorporation.
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Affiliation(s)
- Zachary D Bennett
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, United States
| | - Thomas C Brunold
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI, United States.
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4
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Thaenert A, Sevostyanova A, Chung CZ, Vargas-Rodriguez O, Melnikov SV, Söll D. Engineered mRNA-ribosome fusions for facile biosynthesis of selenoproteins. Proc Natl Acad Sci U S A 2024; 121:e2321700121. [PMID: 38442159 PMCID: PMC10945757 DOI: 10.1073/pnas.2321700121] [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: 12/09/2023] [Accepted: 01/31/2024] [Indexed: 03/07/2024] Open
Abstract
Ribosomes are often used in synthetic biology as a tool to produce desired proteins with enhanced properties or entirely new functions. However, repurposing ribosomes for producing designer proteins is challenging due to the limited number of engineering solutions available to alter the natural activity of these enzymes. In this study, we advance ribosome engineering by describing a novel strategy based on functional fusions of ribosomal RNA (rRNA) with messenger RNA (mRNA). Specifically, we create an mRNA-ribosome fusion called RiboU, where the 16S rRNA is covalently attached to selenocysteine insertion sequence (SECIS), a regulatory RNA element found in mRNAs encoding selenoproteins. When SECIS sequences are present in natural mRNAs, they instruct ribosomes to decode UGA codons as selenocysteine (Sec, U) codons instead of interpreting them as stop codons. This enables ribosomes to insert Sec into the growing polypeptide chain at the appropriate site. Our work demonstrates that the SECIS sequence maintains its functionality even when inserted into the ribosome structure. As a result, the engineered ribosomes RiboU interpret UAG codons as Sec codons, allowing easy and site-specific insertion of Sec in a protein of interest with no further modification to the natural machinery of protein synthesis. To validate this approach, we use RiboU ribosomes to produce three functional target selenoproteins in Escherichia coli by site-specifically inserting Sec into the proteins' active sites. Overall, our work demonstrates the feasibility of creating functional mRNA-rRNA fusions as a strategy for ribosome engineering, providing a novel tool for producing Sec-containing proteins in live bacterial cells.
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Affiliation(s)
- Anna Thaenert
- Department of Molecular Biophysics & Biochemistry, Yale University, New Haven, CT06511
| | | | - Christina Z. Chung
- Department of Molecular Biophysics & Biochemistry, Yale University, New Haven, CT06511
| | | | - Sergey V. Melnikov
- Biosciences Institute, Newcastle University, Newcastle upon TyneNE2 4HH, United Kingdom
- Biosciences Institute, Newcastle University Medical School, Newcastle upon TyneNE2 4HH, United Kingdom
| | - Dieter Söll
- Department of Molecular Biophysics & Biochemistry, Yale University, New Haven, CT06511
- Department of Chemistry, Yale University, New Haven, CT06511
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Weil-Ktorza O, Dhayalan B, Chen YS, Weiss MA, Metanis N. Se-Glargine: Chemical Synthesis of a Basal Insulin Analogue Stabilized by an Internal Diselenide Bridge. Chembiochem 2024; 25:e202300818. [PMID: 38149322 DOI: 10.1002/cbic.202300818] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 12/21/2023] [Accepted: 12/24/2023] [Indexed: 12/28/2023]
Abstract
Insulin has long provided a model for studies of protein folding and stability, enabling enhanced treatment of diabetes mellitus via analogue design. We describe the chemical synthesis of a basal insulin analogue stabilized by substitution of an internal cystine (A6-A11) by a diselenide bridge. The studies focused on insulin glargine (formulated as Lantus® and Toujeo®; Sanofi). Prepared at pH 4 in the presence of zinc ions, glargine exhibits a shifted isoelectric point due to a basic B chain extension (ArgB31 -ArgB32 ). Subcutaneous injection leads to pH-dependent precipitation of a long-lived depot. Pairwise substitution of CysA6 and CysA11 by selenocysteine was effected by solid-phase peptide synthesis; the modified A chain also contained substitution of AsnA21 by Gly, circumventing acid-catalyzed deamidation. Although chain combination of native glargine yielded negligible product, in accordance with previous synthetic studies, the pairwise selenocysteine substitution partially rescued this reaction: substantial product was obtained through repeated combination, yielding a stabilized insulin analogue. This strategy thus exploited both (a) the unique redox properties of selenocysteine in protein folding and (b) favorable packing of an internal diselenide bridge in the native state, once achieved. Such rational optimization of protein folding and stability may be generalizable to diverse disulfide-stabilized proteins of therapeutic interest.
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Affiliation(s)
- Orit Weil-Ktorza
- Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel
| | - Balamurugan Dhayalan
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Yen-Shan Chen
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Michael A Weiss
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Norman Metanis
- Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel
- Casali Center for Applied Chemistry, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel
- The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel
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6
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Morosky P, Comyns C, Nunes LGA, Chung CZ, Hoffmann PR, Söll D, Vargas-Rodriguez O, Krahn N. Dual incorporation of non-canonical amino acids enables production of post-translationally modified selenoproteins. Front Mol Biosci 2023; 10:1096261. [PMID: 36762212 PMCID: PMC9902344 DOI: 10.3389/fmolb.2023.1096261] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Accepted: 01/11/2023] [Indexed: 01/25/2023] Open
Abstract
Post-translational modifications (PTMs) can occur on almost all amino acids in eukaryotes as a key mechanism for regulating protein function. The ability to study the role of these modifications in various biological processes requires techniques to modify proteins site-specifically. One strategy for this is genetic code expansion (GCE) in bacteria. The low frequency of post-translational modifications in bacteria makes it a preferred host to study whether the presence of a post-translational modification influences a protein's function. Genetic code expansion employs orthogonal translation systems engineered to incorporate a modified amino acid at a designated protein position. Selenoproteins, proteins containing selenocysteine, are also known to be post-translationally modified. Selenoproteins have essential roles in oxidative stress, immune response, cell maintenance, and skeletal muscle regeneration. Their complicated biosynthesis mechanism has been a hurdle in our understanding of selenoprotein functions. As technologies for selenocysteine insertion have recently improved, we wanted to create a genetic system that would allow the study of post-translational modifications in selenoproteins. By combining genetic code expansion techniques and selenocysteine insertion technologies, we were able to recode stop codons for insertion of N ε-acetyl-l-lysine and selenocysteine, respectively, into multiple proteins. The specificity of these amino acids for their assigned position and the simplicity of reverting the modified amino acid via mutagenesis of the codon sequence demonstrates the capacity of this method to study selenoproteins and the role of their post-translational modifications. Moreover, the evidence that Sec insertion technology can be combined with genetic code expansion tools further expands the chemical biology applications.
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Affiliation(s)
- Pearl Morosky
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
| | - Cody Comyns
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
| | - Lance G. A. Nunes
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI, United States
| | - Christina Z. Chung
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
| | - Peter R. Hoffmann
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, Honolulu, HI, United States
| | - Dieter Söll
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
- Department of Chemistry, Yale University, New Haven, CT, United States
| | - Oscar Vargas-Rodriguez
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
| | - Natalie Krahn
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
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7
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Chung CZ, Krahn N. The selenocysteine toolbox: A guide to studying the 21st amino acid. Arch Biochem Biophys 2022; 730:109421. [DOI: 10.1016/j.abb.2022.109421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 09/22/2022] [Accepted: 09/26/2022] [Indexed: 11/28/2022]
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8
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Patel A, Mulder DW, Söll D, Krahn N. Harnessing selenocysteine to enhance microbial cell factories for hydrogen production. FRONTIERS IN CATALYSIS 2022; 2. [PMID: 36844461 PMCID: PMC9961374 DOI: 10.3389/fctls.2022.1089176] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Hydrogen is a clean, renewable energy source, that when combined with oxygen, produces heat and electricity with only water vapor as a biproduct. Furthermore, it has the highest energy content by weight of all known fuels. As a result, various strategies have engineered methods to produce hydrogen efficiently and in quantities that are of interest to the economy. To approach the notion of producing hydrogen from a biological perspective, we take our attention to hydrogenases which are naturally produced in microbes. These organisms have the machinery to produce hydrogen, which when cleverly engineered, could be useful in cell factories resulting in large production of hydrogen. Not all hydrogenases are efficient at hydrogen production, and those that are, tend to be oxygen sensitive. Therefore, we provide a new perspective on introducing selenocysteine, a highly reactive proteinogenic amino acid, as a strategy towards engineering hydrogenases with enhanced hydrogen production, or increased oxygen tolerance.
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Affiliation(s)
- Armaan Patel
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
| | - David W Mulder
- National Renewable Energy Laboratory, Biosciences Center, Golden, CO, United States
| | - Dieter Söll
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States.,Department of Chemistry, Yale University, New Haven, CT, United States
| | - Natalie Krahn
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, United States
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9
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Cáceres JC, Bailey CA, Yokoyama K, Greene BL. Selenocysteine substitutions in thiyl radical enzymes. Methods Enzymol 2022; 662:119-141. [DOI: 10.1016/bs.mie.2021.10.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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10
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Mechanisms Affecting the Biosynthesis and Incorporation Rate of Selenocysteine. Molecules 2021; 26:molecules26237120. [PMID: 34885702 PMCID: PMC8659212 DOI: 10.3390/molecules26237120] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Revised: 11/12/2021] [Accepted: 11/18/2021] [Indexed: 11/17/2022] Open
Abstract
Selenocysteine (Sec) is the 21st non-standard proteinogenic amino acid. Due to the particularity of the codon encoding Sec, the selenoprotein synthesis needs to be completed by unique mechanisms in specific biological systems. In this paper, the underlying mechanisms for the biosynthesis and incorporation of Sec into selenoprotein were comprehensively reviewed on five aspects: (i) the specific biosynthesis mechanism of Sec and the role of its internal influencing factors (SelA, SelB, SelC, SelD, SPS2 and PSTK); (ii) the elements (SECIS, PSL, SPUR and RF) on mRNA and their functional mechanisms; (iii) the specificity (either translation termination or translation into Sec) of UGA; (iv) the structure–activity relationship and action mechanism of SelA, SelB, SelC and SelD; and (v) the operating mechanism of two key enzyme systems for inorganic selenium source flow before Sec synthesis. Lastly, the size of the translation initiation interval, other action modes of SECIS and effects of REPS (Repetitive Extragenic Palindromic Sequences) that affect the incorporation efficiency of Sec was also discussed to provide scientific basis for the large-scale industrial fermentation for the production of selenoprotein.
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Evans RM, Krahn N, Murphy BJ, Lee H, Armstrong FA, Söll D. Selective cysteine-to-selenocysteine changes in a [NiFe]-hydrogenase confirm a special position for catalysis and oxygen tolerance. Proc Natl Acad Sci U S A 2021; 118:e2100921118. [PMID: 33753519 PMCID: PMC8020662 DOI: 10.1073/pnas.2100921118] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
In [NiFe]-hydrogenases, the active-site Ni is coordinated by four cysteine-S ligands (Cys; C), two of which are bridging to the Fe(CO)(CN)2 fragment. Substitution of a single Cys residue by selenocysteine (Sec; U) occurs occasionally in nature. Using a recent method for site-specific Sec incorporation into proteins, each of the four Ni-coordinating cysteine residues in the oxygen-tolerant Escherichia coli [NiFe]-hydrogenase-1 (Hyd-1) has been replaced by U to identify its importance for enzyme function. Steady-state solution activity of each Sec-substituted enzyme (on a per-milligram basis) is lowered, although this may reflect the unquantified presence of recalcitrant inactive/immature/misfolded forms. Protein film electrochemistry, however, reveals detailed kinetic data that are independent of absolute activities. Like native Hyd-1, the variants have low apparent KMH2 values, do not produce H2 at pH 6, and display the same onset overpotential for H2 oxidation. Mechanistically important differences were identified for the C576U variant bearing the equivalent replacement found in native [NiFeSe]-hydrogenases, its extreme O2 tolerance (apparent KMH2 and Vmax [solution] values relative to native Hyd-1 of 0.13 and 0.04, respectively) implying the importance of a selenium atom in the position cis to the site where exogenous ligands (H-, H2, O2) bind. Observation of the same unusual electrocatalytic signature seen earlier for the proton transfer-defective E28Q variant highlights the direct role of the chalcogen atom (S/Se) at position 576 close to E28, with the caveat that Se is less effective than S in facilitating proton transfer away from the Ni during H2 oxidation by this enzyme.
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Affiliation(s)
- Rhiannon M Evans
- Inorganic Chemistry Laboratory, University of Oxford, Oxford OX1 3QR, United Kingdom
| | - Natalie Krahn
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511
| | - Bonnie J Murphy
- Inorganic Chemistry Laboratory, University of Oxford, Oxford OX1 3QR, United Kingdom
| | - Harrison Lee
- Inorganic Chemistry Laboratory, University of Oxford, Oxford OX1 3QR, United Kingdom
| | - Fraser A Armstrong
- Inorganic Chemistry Laboratory, University of Oxford, Oxford OX1 3QR, United Kingdom;
| | - Dieter Söll
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511;
- Department of Chemistry, Yale University, New Haven, CT 06520
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