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Claushuis B, Cordfunke RA, de Ru AH, van Angeren J, Baumann U, van Veelen PA, Wuhrer M, Corver J, Drijfhout JW, Hensbergen PJ. Non-prime- and prime-side profiling of Pro-Pro endopeptidase specificity using synthetic combinatorial peptide libraries and mass spectrometry. FEBS J 2024. [PMID: 38767318 DOI: 10.1111/febs.17160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2024] [Revised: 04/25/2024] [Accepted: 05/08/2024] [Indexed: 05/22/2024]
Abstract
A group of bacterial proteases, the Pro-Pro endopeptidases (PPEPs), possess the unique ability to hydrolyze proline-proline bonds in proteins. Since a protease's function is largely determined by its substrate specificity, methods that can extensively characterize substrate specificity are valuable tools for protease research. Previously, we achieved an in-depth characterization of PPEP prime-side specificity. However, PPEP specificity is also determined by the non-prime-side residues in the substrate. To gain a more complete insight into the determinants of PPEP specificity, we characterized the non-prime- and prime-side specificity of various PPEPs using a combination of synthetic combinatorial peptide libraries and mass spectrometry. With this approach, we deepened our understanding of the P3-P3' specificities of PPEP-1 and PPEP-2, while identifying the endogenous substrate of PPEP-2 as the most optimal substrate in our library data. Furthermore, by employing the library approach, we investigated the altered specificity of mutants of PPEP-1 and PPEP-2. Additionally, we characterized a novel PPEP from Anoxybacillus tepidamans, which we termed PPEP-4. Based on structural comparisons, we hypothesized that PPEP-4 displays a PPEP-1-like prime-side specificity, which was substantiated by the experimental data. Intriguingly, another putative PPEP from Clostridioides difficile, CD1597, did not display Pro-Pro endoproteolytic activity. Collectively, we characterized PPEP specificity in detail using our robust peptide library method and, together with additional structural information, provide more insight into the intricate mechanisms that govern protease specificity.
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Affiliation(s)
- Bart Claushuis
- Center for Proteomics and Metabolomics, Leiden University Medical Center, The Netherlands
| | - Robert A Cordfunke
- Department of Immunology, Leiden University Medical Center, The Netherlands
| | - Arnoud H de Ru
- Center for Proteomics and Metabolomics, Leiden University Medical Center, The Netherlands
| | - Jordy van Angeren
- Center for Proteomics and Metabolomics, Leiden University Medical Center, The Netherlands
| | - Ulrich Baumann
- Department of Chemistry, Institute of Biochemistry, University of Cologne, Germany
| | - Peter A van Veelen
- Center for Proteomics and Metabolomics, Leiden University Medical Center, The Netherlands
| | - Manfred Wuhrer
- Center for Proteomics and Metabolomics, Leiden University Medical Center, The Netherlands
| | - Jeroen Corver
- Leiden University Center of Infectious Diseases, Leiden University Medical Center, The Netherlands
| | - Jan W Drijfhout
- Department of Immunology, Leiden University Medical Center, The Netherlands
| | - Paul J Hensbergen
- Center for Proteomics and Metabolomics, Leiden University Medical Center, The Netherlands
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2
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Zorina AA, Novikova GV, Gusev NB, Leusenko AV, Los DA, Klychnikov OI. SpkH (Sll0005) from Synechocystis sp. PCC 6803 is an active Mn 2+-dependent Ser kinase. Biochimie 2023; 213:114-122. [PMID: 37209809 DOI: 10.1016/j.biochi.2023.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 04/23/2023] [Accepted: 05/10/2023] [Indexed: 05/22/2023]
Abstract
Twelve genes for the potential serine-threonine protein kinases (STPKs) have been annotated in the genome of Synechocystis sp. PCC 6803. Based on similarities and distinctive domain organization, they were divided into two clusters: serine/threonine-protein N2-like kinases (PKN2-type) and "activity of bc1 complex" kinases (ABC1-type). While the activity of the PKN2-type kinases have been demonstrated, no ABC1-type kinases activity have hitherto been reported. In this study, a recombinant protein previously annotated as a potential STPK of ABC1-type (SpkH, Sll0005) was expressed and purified to homogeneity. We demonstrated SpkH phosphorylating activity and substrate preference for casein in in vitro assays using [γ-32P]ATP. Detailed analyses of activity showed that Mn2+ had the strongest activation effect. The activity of SpkH was significantly inhibited by heparin and spermine, but not by staurosporine. By means of semi-quantitative mass-spectrometric detection of phosphopeptides, we identified a consensus motif recognized by this kinase - X1X2pSX3E. Thus, we first report here that SpkH of Synechocystis represents a true active serine protein kinase, which shares the properties of casein kinases according to its substrate specificity and sensitivity to some activity effectors.
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Affiliation(s)
- A A Zorina
- K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, Moscow, 127276, Russia.
| | - G V Novikova
- K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, Moscow, 127276, Russia
| | - N B Gusev
- Department of Biochemistry, School of Biology, M.V. Lomonosov Moscow State University, 119991, Moscow, Russia
| | - A V Leusenko
- K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, Moscow, 127276, Russia
| | - D A Los
- K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, Moscow, 127276, Russia
| | - O I Klychnikov
- K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, Moscow, 127276, Russia; Department of Biochemistry, School of Biology, M.V. Lomonosov Moscow State University, 119991, Moscow, Russia
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3
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Claushuis B, Cordfunke RA, de Ru AH, Otte A, van Leeuwen HC, Klychnikov OI, van Veelen PA, Corver J, Drijfhout JW, Hensbergen PJ. In-Depth Specificity Profiling of Endopeptidases Using Dedicated Mix-and-Split Synthetic Peptide Libraries and Mass Spectrometry. Anal Chem 2023; 95:11621-11631. [PMID: 37495545 PMCID: PMC10413326 DOI: 10.1021/acs.analchem.3c01215] [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: 03/20/2023] [Accepted: 07/10/2023] [Indexed: 07/28/2023]
Abstract
Proteases comprise the class of enzymes that catalyzes the hydrolysis of peptide bonds, thereby playing a pivotal role in many aspects of life. The amino acids surrounding the scissile bond determine the susceptibility toward protease-mediated hydrolysis. A detailed understanding of the cleavage specificity of a protease can lead to the identification of its endogenous substrates, while it is also essential for the design of inhibitors. Although many methods for protease activity and specificity profiling exist, none of these combine the advantages of combinatorial synthetic libraries, i.e., high diversity, equimolar concentration, custom design regarding peptide length, and randomization, with the sensitivity and detection power of mass spectrometry. Here, we developed such a method and applied it to study a group of bacterial metalloproteases that have the unique specificity to cleave between two prolines, i.e., Pro-Pro endopeptidases (PPEPs). We not only confirmed the prime-side specificity of PPEP-1 and PPEP-2, but also revealed some new unexpected peptide substrates. Moreover, we have characterized a new PPEP (PPEP-3) that has a prime-side specificity that is very different from that of the other two PPEPs. Importantly, the approach that we present in this study is generic and can be extended to investigate the specificity of other proteases.
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Affiliation(s)
- Bart Claushuis
- Center
for Proteomics and Metabolomics, Leiden
University Medical Center, Leiden, 2333 ZA, The Netherlands
| | - Robert A. Cordfunke
- Department
of Immunology, Leiden University Medical
Center, Leiden, 2333 ZA, The Netherlands
| | - Arnoud H. de Ru
- Center
for Proteomics and Metabolomics, Leiden
University Medical Center, Leiden, 2333 ZA, The Netherlands
| | - Annemarie Otte
- Center
for Proteomics and Metabolomics, Leiden
University Medical Center, Leiden, 2333 ZA, The Netherlands
| | - Hans C. van Leeuwen
- Department
of CBRN Protection, Netherlands Organization
for Applied Scientific Research TNO, Rijswijk, 2280 AA, The Netherlands
| | - Oleg I. Klychnikov
- Department
of Biochemistry, Moscow State University, Moscow 119991, Russian Federation
| | - Peter A. van Veelen
- Center
for Proteomics and Metabolomics, Leiden
University Medical Center, Leiden, 2333 ZA, The Netherlands
| | - Jeroen Corver
- Department
of Medical Microbiology, Leiden University
Medical Center, Leiden, 2333 ZA, The Netherlands
| | - Jan W. Drijfhout
- Department
of Immunology, Leiden University Medical
Center, Leiden, 2333 ZA, The Netherlands
| | - Paul J. Hensbergen
- Center
for Proteomics and Metabolomics, Leiden
University Medical Center, Leiden, 2333 ZA, The Netherlands
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Baharin A, Ting TY, Goh HH. Post-Proline Cleaving Enzymes (PPCEs): Classification, Structure, Molecular Properties, and Applications. PLANTS (BASEL, SWITZERLAND) 2022; 11:1330. [PMID: 35631755 PMCID: PMC9147577 DOI: 10.3390/plants11101330] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 04/29/2022] [Accepted: 05/03/2022] [Indexed: 06/15/2023]
Abstract
Proteases or peptidases are hydrolases that catalyze the breakdown of polypeptide chains into smaller peptide subunits. Proteases exist in all life forms, including archaea, bacteria, protozoa, insects, animals, and plants due to their vital functions in cellular processing and regulation. There are several classes of proteases in the MEROPS database based on their catalytic mechanisms. This review focuses on post-proline cleaving enzymes (PPCEs) from different peptidase families, as well as prolyl endoprotease/oligopeptidase (PEP/POP) from the serine peptidase family. To date, most PPCEs studied are of microbial and animal origins. Recently, there have been reports of plant PPCEs. The most common PEP/POP are members of the S9 family that comprise two conserved domains. The substrate-limiting β-propeller domain prevents unwanted digestion, while the α/β hydrolase catalyzes the reaction at the carboxyl-terminal of proline residues. PPCEs display preferences towards the Pro-X bonds for hydrolysis. This level of selectivity is substantial and has benefited the brewing industry, therapeutics for celiac disease by targeting proline-rich substrates, drug targets for human diseases, and proteomics analysis. Protein engineering via mutagenesis has been performed to improve heat resistance, pepsin-resistant capability, specificity, and protein turnover of PPCEs for pharmacological applications. This review aims to synthesize recent structure-function studies of PPCEs from different families of peptidases to provide insights into the molecular mechanism of prolyl cleaving activity. Despite the non-exhaustive list of PPCEs, this is the first comprehensive review to cover the biochemical properties, biological functions, and biotechnological applications of PPCEs from the diverse taxa.
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van Leeuwen HC, Roelofs D, Corver J, Hensbergen P. Phylogenetic analysis of the bacterial Pro-Pro-endopeptidase domain reveals a diverse family including secreted and membrane anchored proteins. CURRENT RESEARCH IN MICROBIAL SCIENCES 2021; 2:100024. [PMID: 34841315 PMCID: PMC8610288 DOI: 10.1016/j.crmicr.2021.100024] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Revised: 02/19/2021] [Accepted: 02/21/2021] [Indexed: 11/21/2022] Open
Abstract
Bacterial Pro-Pro-endopeptidase (PPEP) is the latest member of the metalloendopeptidase class (E.C. 3.4.24.89). PPEP homologs are found in two firmicutes orders, clostridiales and bacillales spread over 9 genera and more than 130 species. Some PPEP homologs have acquired additional anchor domains that bind noncovalently to various elements of the bacterial peptidoglycan cell wall. Prototype family members, PPEP-1 and PPEP-2, target bacterial surface adhesion proteins, but homologs could target other extracellular proteins.
Pro-Pro-endopeptidases (PPEP, EC 3.4.24.89) are secreted, zinc metalloproteases that have the unusual capacity to cleave a peptide bond between two prolines, a bond that is generally less sensitive to proteolytic cleavage. Two well studied members of the family are PPEP-1 and PPEP-2, produced by Clostridioides difficile, a human pathogen, and Paenibacillus alvei, a bee secondary invader, respectively. Both proteases seem to be involved in mediating bacterial adhesion by cleaving cell surface anchor proteins on the bacterium itself. By using basic alignment and phylogenetic profiling analysis, this work shows that the complete family of proteins that contain a PPEP domain includes proteins from more than 130 species spread over 9 genera. These analyses also suggest that the PPEP domain spread through horizontal gene transfer events between species within the Firmicutes’ classes Bacilli and Clostridia. Bacterial species containing PPEP homologs are found in diverse habitats, varying from human pathogens and gut microbiota to free-living bacteria, which were isolated from various environments, including extreme conditions such as hot springs, desert soil and salt lakes. The phylogenetic tree reveals the relationships between family members and suggests that smaller subgroups could share cleavage specificity, substrates and functional similarity. Except for PPEP-1 and PPEP-2, no cleavage specificity, specific physiological target, or function has been assigned for any of the other PPEP-family members. Some PPEP proteins have acquired additional domains that recognize and bind noncovalently to various elements of the bacterial peptidoglycan cell-wall, anchoring these PPEPs. Secreted or anchored to the cell-wall surface PPEP proteins seem to perform various functions.
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Affiliation(s)
- Hans C van Leeuwen
- Department of CBRN Protection, Netherlands Organization for Applied Scientific Research TNO, Lange Kleiweg 137, 2288 GJ Rijswijk, the Netherlands
| | - Dick Roelofs
- KeyGene, Agro Business Park 90, 6708 PW Wageningen, the Netherlands
| | - Jeroen Corver
- Department of Medical Microbiology, Leiden University Medical Center, Albinusdreef 2, PO Box 9600, 2300 RC Leiden, the Netherlands
| | - Paul Hensbergen
- Center for Proteomics and Metabolomics, Leiden University Medical Center, Albinusdreef 2, PO Box 9600, 2300 RC Leiden, the Netherlands
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6
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A Bioluminescent Sensor for Rapid Detection of PPEP-1, a Clostridioides difficile Biomarker. SENSORS 2021; 21:s21227485. [PMID: 34833562 PMCID: PMC8624784 DOI: 10.3390/s21227485] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Revised: 11/02/2021] [Accepted: 11/03/2021] [Indexed: 11/17/2022]
Abstract
Current assays for Clostridioides difficile in nonhospital settings are outsourced and time-intensive, resulting in both delayed diagnosis and quarantining of infected individuals. We designed a more rapid point-of-care assay featuring a “turn-on” bioluminescent readout of a C. difficile-specific protease, PPEP-1. NanoLuc, a bright and stable luciferase, was “caged” with a PPEP-1-responsive peptide tail that inhibited luminescence. Upon proteolytic cleavage, the peptide was released and NanoLuc activity was restored, providing a visible readout. The bioluminescent sensor detected PPEP-1 concentrations as low as 10 nM. Sensor uncaging was achieved within minutes, and signal was captured using a digital camera. Importantly, the sensor was also functional at ambient temperature and compatible with fecal material, suggesting that it can be readily deployed in a variety of settings.
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Sun P, Zhao Y, Yang L, Ren Z, Zhao W. Environmentally Friendly Quinolones Design for a Two-Way Choice between Biotoxicity and Genotoxicity through Double-Activity 3D-QSAR Model Coupled with the Variation Weighting Method. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2020; 17:E9398. [PMID: 33333906 PMCID: PMC7765274 DOI: 10.3390/ijerph17249398] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Revised: 12/01/2020] [Accepted: 12/14/2020] [Indexed: 11/30/2022]
Abstract
Quinolone (QN) antibiotics are widely used, which lead to their accumulation in soil and toxic effects on ryegrass in pasture. In this study, we employed ryegrass as the research object and selected the total scores of 29 QN molecules docked with two resistant enzyme structures, superoxide dismutase (SOD, PDB ID: 1B06) and proline (Pro, PPEP-2, PDB ID: 6FPC), as dependent variables. The structural parameters of QNs were used as independent variables to construct a QN double-activity 3D-QSAR model for determining the biotoxicity on ryegrass by employing the variation weighting method. This model was constructed to determine modification sites and groups for designing QNs molecules. According to the 3D contour map of the model, by considering enrofloxacin (ENR) and sparfloxacin (SPA) as examples, 23 QN derivatives with low biotoxicity were designed, respectively. The functional properties and environmental friendliness of the QN derivatives were predicted through a two-way selection between biotoxicity and genotoxicity before and after modification; four environmentally friendly derivatives with low biotoxicity and high genotoxicity were screened out. Mixed toxicity index and molecular dynamics methods were used to verify the combined toxicity mechanism of QNs on ryegrass before and after modification. By simulating the combined pollution of ENR and its derivatives in different soils (farmland, garden, and woodland), the types of combined toxicity were determined as partial additive and synergistic. Binding energies were calculated using molecular dynamics. The designed QN derivatives with low biotoxicity, high genotoxicity, and environmental friendliness can highly reduce the combined toxicity on ryegrass and can be used as theoretic reserves to replace QN antibiotics.
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Affiliation(s)
- Peixuan Sun
- College of New Energy and Environment, Jilin University, Changchun 130012, China; (P.S.); (L.Y.)
| | - Yuanyuan Zhao
- College of Environmental Science and Engineering, North China Electric Power University, Beijing 102206, China;
| | - Luze Yang
- College of New Energy and Environment, Jilin University, Changchun 130012, China; (P.S.); (L.Y.)
| | - Zhixing Ren
- College of Forestry, Northeast Forestry University, Harbin 150040, China;
| | - Wenjin Zhao
- College of New Energy and Environment, Jilin University, Changchun 130012, China; (P.S.); (L.Y.)
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Doan CT, Tran TN, Wang CL, Wang SL. Microbial Conversion of Shrimp Heads to Proteases and Chitin as an Effective Dye Adsorbent. Polymers (Basel) 2020; 12:E2228. [PMID: 32998333 PMCID: PMC7601101 DOI: 10.3390/polym12102228] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Revised: 09/26/2020] [Accepted: 09/26/2020] [Indexed: 02/06/2023] Open
Abstract
As a green and effective technique in the production of a large number of valuable products, the microbial conversion of chitinous fishery wastes is receiving much attention. In this study, protease production using the Paenibacillus mucilaginosus TKU032 strain was conducted on culture media containing several common types of chitinous fishery by-products serving as the carbon and nitrogen (C/N) nutrition source. Among the chitinous wastes, 1.5% (w/v) shrimp head powder (SHP) was found to be the most appropriate nutritional source for protease production when a maximal enzyme activity of 3.14 ± 0.1 U/mL was observed on the 3rd day of the culture period. The molecular mass of P. mucilaginosus TKU032 protease was estimated to be nearly 32 kDa by the polyacrylamide gel electrophoresis method. The residual SHP obtained from the culture medium was also considered to be utilized for chitin extraction. The deproteinization rate of the fermentation was estimated to be 45%, and the chitin obtained from fermented SHP (fSHP) displayed a similar characteristic Fourier-transform infrared spectroscopy (FTIR) profile as that from SHP. In addition, SHP, fSHP, and chitins obtained from SHP and fSHP were investigated for their adsorptive capacity of nine types of dyes, and chitin obtained from fSHP displayed a good adsorption rate on Congo Red and Red No. 7, at 99% and 97%, respectively. In short, the results provide potential support for the utilization of SHP in the production of P. mucilaginosus TKU032 protease via the fermentation as well as the preparation of chitin from fSHP as an effective dye adsorbent.
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Affiliation(s)
- Chien Thang Doan
- Department of Natural Science and Technology, Tay Nguyen University, Buon Ma Thuot 630000, Vietnam; (C.T.D.); (T.N.T.)
- Department of Chemistry, Tamkang University, New Taipei City 25137, Taiwan
| | - Thi Ngoc Tran
- Department of Natural Science and Technology, Tay Nguyen University, Buon Ma Thuot 630000, Vietnam; (C.T.D.); (T.N.T.)
- Department of Chemistry, Tamkang University, New Taipei City 25137, Taiwan
| | - Chuan-Lu Wang
- Department of Fashion Beauty Design, Lan Yang Institute of Technology, Yilan County 26141, Taiwan;
| | - San-Lang Wang
- Department of Chemistry, Tamkang University, New Taipei City 25137, Taiwan
- Life Science Development Center, Tamkang University, New Taipei City 25137, Taiwan
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Pichlo C, Juetten L, Wojtalla F, Schacherl M, Diaz D, Baumann U. Molecular determinants of the mechanism and substrate specificity of Clostridium difficile proline-proline endopeptidase-1. J Biol Chem 2019; 294:11525-11535. [PMID: 31182482 DOI: 10.1074/jbc.ra119.009029] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 05/27/2019] [Indexed: 11/06/2022] Open
Abstract
Pro-Pro endopeptidase-1 (PPEP-1) is a secreted metalloprotease from the bacterial pathogen Clostridium difficile that cleaves two endogenous adhesion proteins. PPEP-1 is therefore important for bacterial motility and hence for efficient gut colonization during infection. PPEP-1 exhibits a unique specificity for Pro-Pro peptide bonds within the consensus sequence VNP↓PVP. In this study, we combined information from crystal and NMR structures with mutagenesis and enzyme kinetics to investigate the mechanism and substrate specificity of PPEP-1. Our analyses revealed that the substrate-binding cleft of PPEP-1 is shaped complementarily to the major conformation of the substrate in solution. We found that it possesses features that accept a tertiary amide and help discriminate P1' residues by their amide hydrogen bond-donating potential. We also noted that residues Lys-101, Trp-103, and Glu-184 are crucial for proteolytic activity. Upon substrate binding, these residues position a flexible loop over the substrate-binding cleft and modulate the second coordination sphere of the catalytic zinc ion. On the basis of these findings, we propose an induced-fit model in which prestructured substrates are recognized followed by substrate positioning within the active-site cleft and a concomitant increase in the Lewis acidity of the catalytic Zn2+ ion. In conclusion, our findings provide detailed structural and mechanistic insights into the substrate recognition and specificity of PPEP-1 from the common gut pathogen C. difficile.
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Affiliation(s)
- Christian Pichlo
- Department of Chemistry, Institute of Biochemistry, University of Cologne, 50674 Cologne, Germany
| | - Linda Juetten
- Department of Chemistry, Institute of Organic Chemistry, University of Cologne, 50939 Cologne, Germany
| | - Fabian Wojtalla
- Department of Chemistry, Institute of Biochemistry, University of Cologne, 50674 Cologne, Germany
| | - Magdalena Schacherl
- Department of Chemistry, Institute of Biochemistry, University of Cologne, 50674 Cologne, Germany
| | - Dolores Diaz
- Department of Chemistry, Institute of Organic Chemistry, University of Cologne, 50939 Cologne, Germany
| | - Ulrich Baumann
- Department of Chemistry, Institute of Biochemistry, University of Cologne, 50674 Cologne, Germany
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