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Sadarangani V, Kalia A, Kausar T, Murarka P, Sau AK. Effect of the Macromolecular Crowding Agents on the Structure and Function of Human Arginase-I, a Therapeutically Important Enzyme. J Phys Chem B 2023; 127:8749-8761. [PMID: 37796726 DOI: 10.1021/acs.jpcb.3c02940] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/07/2023]
Abstract
Macromolecular crowding has been known to influence the structure and function of many enzymes through excluded volume effects and/or soft interactions. Here, we employed two synthetic macromolecular crowders, Dextrans and poly(ethylene glycol)s (PEGs) with varying molecular masses, to examine how they affected the structure and function of a therapeutically important enzyme, human arginase-I that catalyzes the conversion of l-arginine to l-ornithine and urea. Except at greater concentrations of Dextran 200, Dextrans were observed to slightly reduce the enzymatic activity, indicating that they exert their influence mainly through the excluded volume effects. Similar outcomes were seen with PEGs, with the exception of PEG 1000, where the activity decreased with increasing PEG concentrations, showing the maximum effect at a 20 g/L concentration. This finding suggests that the enzyme function is reduced by the soft interactions of this macromolecule with the enzyme, supported by the binding measurement. Secondary and local tertiary structures and thermodynamic stability were also affected, suggesting that PEG 1000 has an impact on the protein's structure. Furthermore, molecular dynamics simulation studies suggest that the catalytic pocket is disturbed, presumably by the unwinding of neighboring helix 9. As a result, the positioning of nearby Glu277 is altered, which prevents His141 and Glu277 from making contact. This hampers the proton transfer from the catalytic His141 to the intermediate species to form ornithine, a crucial step for the substrate hydrolysis reaction by this arginase. Overall, the knowledge gained from this study might be helpful for understanding how different enzymes work in a crowded/cellular environment.
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Affiliation(s)
- Vineet Sadarangani
- Protein Engineering Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110067, India
| | - Anjali Kalia
- Protein Engineering Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110067, India
| | - Tasneem Kausar
- Protein Engineering Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110067, India
| | - Pooja Murarka
- Protein Engineering Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110067, India
| | - Apurba Kumar Sau
- Protein Engineering Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110067, India
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2
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Sarkar D, Sau AK. Illuminating the structure-function landscape of an evolutionary nonconserved motif in the arginases of Helicobacter gastric pathogens. IUBMB Life 2023; 75:782-793. [PMID: 37086465 DOI: 10.1002/iub.2728] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2022] [Accepted: 04/03/2023] [Indexed: 04/24/2023]
Abstract
The bimetallic enzyme arginase catalyses the conversion of L-arginine to L-ornithine and urea. In Helicobacter pylori (a known human gastric pathogen), this enzyme is an important virulence factor. In spite of the conservation of the catalytic and the metal-binding residues, the H. pylori homolog possesses a 13-residue motif (-153 ESEEKAWQKLCSL165 -) present in the middle of the protein sequence, whose role was recently elucidated. Despite several reviews available on arginases, no report has thoroughly illustrated the underlying basis for the importance of the above motif of the H. pylori enzyme in structure and function. In this review, we systematically describe a mechanistic basis for its importance in structure and function based on the known data. This motif of the H. pylori enzyme is present exclusively in the arginases of other Helicobacter gastric pathogens, where the critical residues are conserved, implying that the nonconserved stretch has been selected during the evolution of the enzyme in these gastric pathogens in a specific manner to perform its role in the structure and function. The combined information can be useful for understanding the function of arginases in other Helicobacter gastric pathogens. Additionally, this knowledge can be utilised to screen and design new small molecule inhibitors, specific to the arginases of these pathogens.
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Affiliation(s)
- Ditsa Sarkar
- Protein Engineering Laboratory, National Institute of Immunology, New Delhi, Delhi, India
| | - Apurba Kumar Sau
- Protein Engineering Laboratory, National Institute of Immunology, New Delhi, Delhi, India
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3
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Hernández VM, Arteaga A, Dunn MF. Diversity, properties and functions of bacterial arginases. FEMS Microbiol Rev 2021; 45:6308370. [PMID: 34160574 DOI: 10.1093/femsre/fuab034] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 06/17/2021] [Indexed: 02/07/2023] Open
Abstract
The metalloenzyme arginase hydrolyzes L-arginine to produce L-ornithine and urea. In bacteria, arginase has important functions in basic nitrogen metabolism and redistribution, production of the key metabolic precursor L-ornithine, stress resistance and pathogenesis. We describe the regulation and specific functions of the arginase pathway as well as summarize key characteristics of related arginine catabolic pathways. The use of arginase-derived ornithine as a precursor molecule is reviewed. We discuss the biochemical and transcriptional regulation of arginine metabolism, including arginase, with the latter topic focusing on the RocR and AhrC transcriptional regulators in the model organism Bacillus subtilis. Finally, we consider similarities and contrasts in the structure and catalytic mechanism of the arginases from Bacillus caldovelox and Helicobacter pylori. The overall aim of this review is to provide a panorama of the diversity of physiological functions, regulation, and biochemical features of arginases in a variety of bacterial species.
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Affiliation(s)
- Victor M Hernández
- Programa de Genómica Funcional de Procariotes, Centro de Ciencias Genómicas-Universidad Nacional Autonoma de México, Cuernavaca, Morelos, C.P. 62210, Mexico
| | - Alejandra Arteaga
- Programa de Genómica Funcional de Procariotes, Centro de Ciencias Genómicas-Universidad Nacional Autonoma de México, Cuernavaca, Morelos, C.P. 62210, Mexico
| | - Michael F Dunn
- Programa de Genómica Funcional de Procariotes, Centro de Ciencias Genómicas-Universidad Nacional Autonoma de México, Cuernavaca, Morelos, C.P. 62210, Mexico
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4
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An evolutionary non-conserved motif in Helicobacter pylori arginase mediates positioning of the loop containing the catalytic residue for catalysis. Biochem J 2021; 478:871-894. [PMID: 33480396 DOI: 10.1042/bcj20200978] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 01/21/2021] [Accepted: 01/22/2021] [Indexed: 01/01/2023]
Abstract
The binuclear metalloenzyme Helicobacter pylori arginase is important for pathogenesis of the bacterium in the human stomach. Despite conservation of the catalytic residues, this single Trp enzyme has an insertion sequence (-153ESEEKAWQKLCSL165-) that is extremely crucial to function. This sequence contains the critical residues, which are conserved in the homolog of other Helicobacter gastric pathogens. However, the underlying basis for the role of this motif in catalytic function is not completely understood. Here, we used biochemical, biophysical and molecular dynamics simulations studies to determine that Glu155 of this stretch interacts with both Lys57 and Ser152. These interactions are essential for positioning of the motif through Trp159, which is located near Glu155 (His122-Trp159-Tyr125 contact is essential to tertiary structural integrity). The individual or double mutation of Lys57 and Ser152 to Ala considerably reduces catalytic activity with Lys57 to Ala being more significant, indicating they are crucial to function. Our data suggest that the Lys57-Glu155-Ser152 interaction influences the positioning of the loop containing the catalytic His133 so that this His can participate in catalysis, thereby providing a mechanistic understanding into the role of this motif in catalytic function. Lys57 was also found only in the arginases of other Helicobacter gastric pathogens. Based on the non-conserved motif, we found a new molecule, which specifically inhibits this enzyme. Thus, the present study not only provides a molecular basis into the role of this motif in function, but also offers an opportunity for the design of inhibitors with greater efficacy.
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5
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Kelley BR, Lu J, Haley KP, Gaddy JA, Johnson JG. Metal homeostasis in pathogenic Epsilonproteobacteria: mechanisms of acquisition, efflux, and regulation. Metallomics 2021; 13:mfaa002. [PMID: 33570133 PMCID: PMC8043183 DOI: 10.1093/mtomcs/mfaa002] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 11/25/2020] [Accepted: 12/03/2020] [Indexed: 12/14/2022]
Abstract
Epsilonproteobacteria are a diverse class of eubacteria within the Proteobacteria phylum that includes environmental sulfur-reducing bacteria and the human pathogens, Campylobacter jejuni and Helicobacter pylori. These pathogens infect and proliferate within the gastrointestinal tracts of multiple animal hosts, including humans, and cause a variety of disease outcomes. While infection of these hosts provides nutrients for the pathogenic Epsilonproteobacteria, many hosts have evolved a variety of strategies to either sequester metals from the invading pathogen or exploit the toxicity of metals and drive their accumulation as an antimicrobial strategy. As a result, C. jejuni and H. pylori have developed mechanisms to sense changes in metal availability and regulate their physiology in order to respond to either metal limitation or accumulation. In this review, we will discuss the challenges of metal availability at the host-pathogen interface during infection with C. jejuni and H. pylori and describe what is currently known about how these organisms alter their gene expression and/or deploy bacterial virulence factors in response to these environments.
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Affiliation(s)
- Brittni R Kelley
- Department of Microbiology, University of Tennessee, Knoxville, TN, USA
| | - Jacky Lu
- Department of Pathology, Microbiology and Immunology, Vanderbilt University, Nashville, TN, USA
| | - Kathryn P Haley
- Department of Biology, Grand Valley State University, Grand Rapids, MI, USA
| | - Jennifer A Gaddy
- Department of Pathology, Microbiology and Immunology, Vanderbilt University, Nashville, TN, USA
- Tennessee Valley Healthcare Systems, Department of Veterans Affairs, Nashville, TN, USA
- Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
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6
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The Effects of the Metal Ion Substitution into the Active Site of Metalloenzymes: A Theoretical Insight on Some Selected Cases. Catalysts 2020. [DOI: 10.3390/catal10091038] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
A large number of enzymes need a metal ion to express their catalytic activity. Among the different roles that metal ions can play in the catalytic event, the most common are their ability to orient the substrate correctly for the reaction, to exchange electrons in redox reactions, to stabilize negative charges. In many reactions catalyzed by metal ions, they behave like the proton, essentially as Lewis acids but are often more effective than the proton because they can be present at high concentrations at neutral pH. In an attempt to adapt to drastic environmental conditions, enzymes can take advantage of the presence of many metal species in addition to those defined as native and still be active. In fact, today we know enzymes that contain essential bulk, trace, and ultra-trace elements. In this work, we report theoretical results obtained for three different enzymes each of which contains different metal ions, trying to highlight any differences in their working mechanism as a function of the replacement of the metal center at the active site.
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7
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Hwangbo SA, Kim JW, Jung SJ, Jin KS, Lee JO, Kim JS, Park SY. Characterization of a Dimeric Arginase From Zymomonas mobilis ZM4. Front Microbiol 2019; 10:2755. [PMID: 32038508 PMCID: PMC6988801 DOI: 10.3389/fmicb.2019.02755] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 11/12/2019] [Indexed: 12/23/2022] Open
Abstract
Many organisms have genes to protect themselves from toxic conditions such as high ethanol and/or ammonia concentrations. When a high ethanol condition is induced to Zymomonas mobilis ZM4, a representative ethanologenic organism, this bacterium overexpresses several genes to overcome this ethanol stress. Among them, we characterized a gene product annotated as an arginase (zmARG) from Z. mobilis ZM4. Even though all of the arginase-determining sequence motifs are not strictly conserved in zmARG, this enzyme converts L-arginine to urea and L-ornithine in the presence of a divalent manganese ion. The revealed high-resolution crystal structure of zmARG shows that it has a typical globular α/β arginase fold with a protruded C-terminal helix. Two zinc ions reside in the active site, where one metal ion is penta-coordinated and the other has six ligands, discerning this zmARG from the reported arginases with two hexa-liganded metal ions. zmARG forms a dimeric structure in solution as well as in the crystalline state. The dimeric assembly of zmARG is formed mainly by interaction formed between the C-terminal α-helix of one molecule and the α/β hydrolase fold of another molecule. The presented findings demonstrate the first reported dimeric arginase formed by the C-terminal tail and has two metal ions coordinated by different number of ligands.
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Affiliation(s)
- Seung-A Hwangbo
- Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, South Korea.,Institute of Membrane Proteins, Pohang University of Science and Technology, Pohang, South Korea
| | - Ji-Won Kim
- Department of Chemistry, Chonnam National University, Gwangju, South Korea
| | - Sun-Ju Jung
- Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, South Korea
| | - Kyeong Sik Jin
- Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, South Korea
| | - Jie-Oh Lee
- Institute of Membrane Proteins, Pohang University of Science and Technology, Pohang, South Korea
| | - Jeong-Sun Kim
- Department of Chemistry, Chonnam National University, Gwangju, South Korea
| | - Suk-Youl Park
- Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, South Korea
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8
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Metal ions-induced stability and function of bimetallic human arginase-I, a therapeutically important enzyme. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2018; 1866:1153-1164. [DOI: 10.1016/j.bbapap.2018.08.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Revised: 07/21/2018] [Accepted: 08/20/2018] [Indexed: 11/16/2022]
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9
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Alam M, Srivastava A, Dutta A, Sau AK. Biochemical and biophysical studies ofHelicobacter pyloriarginine decarboxylase, an enzyme important for acid adaptation in host. IUBMB Life 2018; 70:658-669. [DOI: 10.1002/iub.1754] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Accepted: 03/26/2018] [Indexed: 01/06/2023]
Affiliation(s)
- Mashkoor Alam
- National Institute of Immunology, Aruna Asaf Ali Marg; New Delhi Delhi India
| | - Abhishek Srivastava
- National Institute of Immunology, Aruna Asaf Ali Marg; New Delhi Delhi India
| | - Ankita Dutta
- National Institute of Immunology, Aruna Asaf Ali Marg; New Delhi Delhi India
| | - Apurba Kumar Sau
- National Institute of Immunology, Aruna Asaf Ali Marg; New Delhi Delhi India
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10
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George G, Kombrabail M, Raninga N, Sau AK. Arginase of Helicobacter Gastric Pathogens Uses a Unique Set of Non-catalytic Residues for Catalysis. Biophys J 2017; 112:1120-1134. [PMID: 28355540 DOI: 10.1016/j.bpj.2017.02.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Revised: 01/26/2017] [Accepted: 02/06/2017] [Indexed: 12/12/2022] Open
Abstract
Helicobacter pylori arginase, a bimetallic enzyme, is crucial for pathogenesis of the bacterium in human stomach. Despite conservation of the signature motifs in all arginases, the H. pylori homolog has a non-conserved motif (153ESEEKAWQKLCSL165), whose role was recently shown to be critical for its stability and function. The sequence analysis also reveals the presence of this motif with critical residues in the homolog of other Helicobacter gastric pathogens. However, the underlying mechanism for its significance in catalytic function is not clearly understood. Using H. pylori arginase, our studies reveal that the interactions of His122 and Tyr125 with Trp159 are indispensable for tertiary structural intactness through optimal positioning of the motif and thus for the catalytic function. The single and double mutants of His122 and Tyr125 not only enhanced the solvent accessibility and conformational flexibility of Trp159 in the holo protein, but also showed complete loss of catalytic activity. An intact bimetallic center and unaltered substrate binding indicate that proper positioning of the motif by aromatic-aromatic contact is vital for the generation of a catalytically active conformation. Additionally, the metal ions provide higher stability to the holo protein. We also identified the presence of these two residues exclusively in arginase of other Helicobacter gastric pathogens, which may have similar function. Therefore, to the best of our knowledge, these findings highlight for the first time that arginase of all Helicobacter gastric pathogens utilizes a unique non-catalytic triad for catalysis, which could be exploited for therapeutics.
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Affiliation(s)
- Ginto George
- National Institute of Immunology, New Delhi, India
| | - Mamata Kombrabail
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai, India
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11
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Haley KP, Gaddy JA. Metalloregulation of Helicobacter pylori physiology and pathogenesis. Front Microbiol 2015; 6:911. [PMID: 26388855 PMCID: PMC4557348 DOI: 10.3389/fmicb.2015.00911] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Accepted: 08/19/2015] [Indexed: 12/23/2022] Open
Abstract
Helicobacter pylori is a Gram-negative spiral-shaped bacterium that colonizes over half of the world's population. Chronic H. pylori infection is associated with increased risk for numerous disease outcomes including gastritis, dysplasia, neoplasia, B-cell lymphoma of mucosal-associated lymphoid tissue (MALT lymphoma), and invasive adenocarcinoma. The complex interactions that occur between pathogen and host are dynamic and exquisitely regulated, and the relationship between H. pylori and its human host are no exception. To successfully colonize, and subsequently persist, within the human stomach H. pylori must temporally regulate numerous genes to ensure localization to the gastric lumen and coordinated expression of virulence factors to subvert the host's innate and adaptive immune response. H. pylori achieves this precise gene regulation by sensing subtle environmental changes including host-mediated alterations in nutrient availability and responding with dramatic global changes in gene expression. Recent studies revealed that the presence or absence of numerous metal ions encountered in the lumen of the stomach, or within host tissues, including nickel, iron, copper and zinc, can influence regulatory networks to alter gene expression in H. pylori. These expression changes modulate the deployment of bacterial virulence factors that can ultimately influence disease outcome. In this review we will discuss the environmental stimuli that are detected by H. pylori as well as the trans regulatory elements, specifically the transcription regulators and transcription factors, that allow for these significant transcriptional shifts.
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Affiliation(s)
- Kathryn P Haley
- Tennessee Valley Healthcare Services, Department of Veterans Affairs Nashville, TN, USA
| | - Jennifer A Gaddy
- Department of Medicine, Vanderbilt University School of Medicine Nashville, TN, USA ; Tennessee Valley Healthcare Services, Department of Veterans Affairs Nashville, TN, USA
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12
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Zhang X, Zhang J, Zhang R, Guo Y, Wu C, Mao X, Guo G, Zhang Y, Li D, Zou Q. Structural, enzymatic and biochemical studies on Helicobacter pylori arginase. Int J Biochem Cell Biol 2013; 45:995-1002. [PMID: 23454280 DOI: 10.1016/j.biocel.2013.02.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Revised: 01/25/2013] [Accepted: 02/11/2013] [Indexed: 11/25/2022]
Abstract
Arginase is an enzyme involved in the last step of the urea cycle, where it catalyses the hydrolysis of l-arginine to generate l-ornithine and urea. Compared to the well-characterised arginases from animals, yeast and other bacteria, Helicobacter pylori arginase, or RocF, is unique in at least three aspects. Firstly, it has been identified as an important factor in evasion of the host's immune system and thus contributes to persistent infection by the bacterium. Secondly, the optimal catalytic conditions of RocF are different from those of other arginases. Finally, sequence alignment indicates that RocF possesses considerable differences at its N- and C-terminal from other arginases and harbours an insertion of 13 residues in the middle of the sequence. To better understand these unique biochemical and enzymatic properties, we therefore have embarked on determining the structure of RocF. In this study, the crystal structure of RocF was solved with the molecular replacement method. Based on the structure and systematic mutagenesis studies, we confirmed that the inserted residues form a helix that was not observed in other arginases and was able to raise the arginase activity by 30% probably by change the conformation of the substrate binding pocket. Six residues were involved in Mn(2+) binding, all of which were essential for arginase activity. The C-terminal motif is not sufficient in establishing the oligomeric state of RocF, and no disulphide bonds were observed in RocF.
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Affiliation(s)
- Xiaoli Zhang
- Department of Clinical Microbiology and Immunology, College of Medical Laboratory, Third Military Medical University, Chongqing 400038, China
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13
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Srivastava A, Meena SK, Alam M, Nayeem SM, Deep S, Sau AK. Structural and Functional Insights into the Regulation of Helicobacter pylori Arginase Activity by an Evolutionary Nonconserved Motif. Biochemistry 2013; 52:508-19. [DOI: 10.1021/bi301421v] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Abhishek Srivastava
- National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110 067,
India
| | - Shiv Kumar Meena
- National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110 067,
India
| | - Mashkoor Alam
- National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110 067,
India
| | - Shahid M. Nayeem
- Department of Chemistry, Indian Institute of Technology, New Delhi 110 016,
India
| | - Shashank Deep
- Department of Chemistry, Indian Institute of Technology, New Delhi 110 016,
India
| | - Apurba Kumar Sau
- National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110 067,
India
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Marino T, Russo N, Toscano M. What occurs by replacing Mn2+ with Co2+ in human arginase I: first-principles computational analysis. Inorg Chem 2012; 52:655-9. [PMID: 23273171 DOI: 10.1021/ic301703t] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The reaction mechanism of the dinuclear cobalt enzyme arginase is investigated using density functional theory. As an arginase-containing binuclear Mn(2)(2+) cluster, it catalyzes the hydrolysis of L-arginine in L-ornithine and urea. The bridging hydroxide is capable of performing nucleophilic attack on the iminium carbon ion from its bridging position, resulting in the formation of a tetrahedral intermediate, as was already obtained in a previous theoretical study on the manganese enzyme. Our theoretical investigation allows us to obtain an accurate potential energy profile and confirms that the coordination mode of the substrate to the dimetallic center is quite similar to that present in the manganese enzyme. In agreement with the experimental observations, our results show that both Mn- and Co-containing enzymes catalyze the same reaction with quite comparable energy barriers.
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Affiliation(s)
- Tiziana Marino
- Dipartimento di Chimica and Centro di Calcolo ad Alte Prestazioni per Elaborazioni Parallele e Distribuite, Universitá della Calabria, I-87030 Arcavacata di Rende (CS), Italy.
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