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Sunder S, Bhandari K, Sounkaria S, Vyas M, Singh BP, Chandra P. Antibiotics and nano-antibiotics in treatment of lung infection: In management of COVID-19. Microb Pathog 2023; 184:106356. [PMID: 37743025 DOI: 10.1016/j.micpath.2023.106356] [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: 05/20/2023] [Revised: 09/06/2023] [Accepted: 09/13/2023] [Indexed: 09/26/2023]
Abstract
The world has witnessed the cruelty of COVID-19 disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The association of COVID-19 with other secondary and bacterial co-infections has tremendously contributed to lung infections. An increased probability of having a secondary lung infection was observed among the post-COVID patients. The treatment of antibiotics has ameliorated the mortality rate. However, the stewardship of antibiotic treatment was linked to increased organ failure. Therefore, the paper discusses the interactions between the virus and host through the ACE2 receptors that contribute to COVID-19 development. Furthermore, the paper provides an invaluable compendium history of SARS-CoV-2 genomic composition. It revolves around most classes of antibiotics used to treat COVID-19 disease and post-COVID lung infections with the complete mechanism. This binds with the exertion of the antibiotics for bacterial infection associated with COVID-19 patients and how beneficial and effective responses have been recorded for the treatment. The application of nanotechnology and possible approaches of nanomedicines is also discussed to its potential usage.
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Affiliation(s)
- Sushant Sunder
- Department of Biotechnology, Delhi Technological University, New Delhi, 110042, India; Department of Bioengineering, University of California San Diego, La Jolla, CA 92093, USA
| | - Kriti Bhandari
- Department of Biotechnology, Delhi Technological University, New Delhi, 110042, India
| | - Shruti Sounkaria
- Department of Biotechnology, Delhi Technological University, New Delhi, 110042, India
| | - Manjari Vyas
- Department of Biotechnology, Delhi Technological University, New Delhi, 110042, India
| | - Bhupendra Pratap Singh
- Department of Environmental Studies, Central University of Haryana, Jant-Pali, Mahendergarh, Haryana, 123031, India
| | - Prakash Chandra
- Department of Biotechnology, Delhi Technological University, New Delhi, 110042, India.
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Lang PA, Raj R, Tumber A, Lohans CT, Rabe P, Robinson CV, Brem J, Schofield CJ. Studies on enmetazobactam clarify mechanisms of widely used β-lactamase inhibitors. Proc Natl Acad Sci U S A 2022; 119:e2117310119. [PMID: 35486701 PMCID: PMC9170034 DOI: 10.1073/pnas.2117310119] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2021] [Accepted: 03/14/2022] [Indexed: 11/18/2022] Open
Abstract
β-Lactams are the most important class of antibacterials, but their use is increasingly compromised by resistance, most importantly via serine β-lactamase (SBL)-catalyzed hydrolysis. The scope of β-lactam antibacterial activity can be substantially extended by coadministration with a penicillin-derived SBL inhibitor (SBLi), i.e., the penam sulfones tazobactam and sulbactam, which are mechanism-based inhibitors working by acylation of the nucleophilic serine. The new SBLi enmetazobactam, an N-methylated tazobactam derivative, has recently completed clinical trials. Biophysical studies on the mechanism of SBL inhibition by enmetazobactam reveal that it inhibits representatives of all SBL classes without undergoing substantial scaffold fragmentation, a finding that contrasts with previous reports on SBL inhibition by tazobactam and sulbactam. We therefore reinvestigated the mechanisms of tazobactam and sulbactam using mass spectrometry under denaturing and nondenaturing conditions, X-ray crystallography, and NMR spectroscopy. The results imply that the reported extensive fragmentation of penam sulfone–derived acyl–enzyme complexes does not substantially contribute to SBL inhibition. In addition to observation of previously identified inhibitor-induced SBL modifications, the results reveal that prolonged reaction of penam sulfones with SBLs can induce dehydration of the nucleophilic serine to give a dehydroalanine residue that undergoes reaction to give a previously unobserved lysinoalanine cross-link. The results clarify the mechanisms of action of widely clinically used SBLi, reveal limitations on the interpretation of mass spectrometry studies concerning mechanisms of SBLi, and will inform the development of new SBLi working by reaction to form hydrolytically stable acyl–enzyme complexes.
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Affiliation(s)
- Pauline A. Lang
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
- Ineos Oxford Institute for Antimicrobial Research, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Ritu Raj
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Anthony Tumber
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
- Ineos Oxford Institute for Antimicrobial Research, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Christopher T. Lohans
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
- Ineos Oxford Institute for Antimicrobial Research, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Patrick Rabe
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
- Ineos Oxford Institute for Antimicrobial Research, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Carol V. Robinson
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
- Kavli Institute for Nanoscience Discovery, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Jürgen Brem
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
- Ineos Oxford Institute for Antimicrobial Research, University of Oxford, Oxford OX1 3TA, United Kingdom
| | - Christopher J. Schofield
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
- Ineos Oxford Institute for Antimicrobial Research, University of Oxford, Oxford OX1 3TA, United Kingdom
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Mora-Ochomogo M, Lohans CT. β-Lactam antibiotic targets and resistance mechanisms: from covalent inhibitors to substrates. RSC Med Chem 2021; 12:1623-1639. [PMID: 34778765 PMCID: PMC8528271 DOI: 10.1039/d1md00200g] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Accepted: 07/25/2021] [Indexed: 12/24/2022] Open
Abstract
The β-lactams are the most widely used antibacterial agents worldwide. These antibiotics, a group that includes the penicillins and cephalosporins, are covalent inhibitors that target bacterial penicillin-binding proteins and disrupt peptidoglycan synthesis. Bacteria can achieve resistance to β-lactams in several ways, including the production of serine β-lactamase enzymes. While β-lactams also covalently interact with serine β-lactamases, these enzymes are capable of deacylating this complex, treating the antibiotic as a substrate. In this tutorial-style review, we provide an overview of the β-lactam antibiotics, focusing on their covalent interactions with their target proteins and resistance mechanisms. We begin by describing the structurally diverse range of β-lactam antibiotics and β-lactamase inhibitors that are currently used as therapeutics. Then, we introduce the penicillin-binding proteins, describing their functions and structures, and highlighting their interactions with β-lactam antibiotics. We next describe the classes of serine β-lactamases, exploring some of the mechanisms by which they achieve the ability to degrade β-lactams. Finally, we introduce the l,d-transpeptidases, a group of bacterial enzymes involved in peptidoglycan synthesis which are also targeted by β-lactam antibiotics. Although resistance mechanisms are now prevalent for all antibiotics in this class, past successes in antibiotic development have at least delayed this onset of resistance. The β-lactams continue to be an essential tool for the treatment of infectious disease, and recent advances (e.g., β-lactamase inhibitor development) will continue to support their future use.
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Affiliation(s)
| | - Christopher T Lohans
- Department of Biomedical and Molecular Sciences, Queen's University Kingston ON K7L 3N6 Canada
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Awasthi A, Singh SK, Kumar B, Gulati M, Kumar R, Wadhwa S, Khursheed R, Corrie L, Kr A, Kumar R, Patni P, Kaur J, Vishwas S, Yadav A. Treatment Strategies Against Diabetic Foot Ulcer: Success so Far and the Road Ahead. Curr Diabetes Rev 2021; 17:421-436. [PMID: 33143613 DOI: 10.2174/1573399816999201102125537] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Revised: 10/15/2020] [Accepted: 10/20/2020] [Indexed: 11/22/2022]
Abstract
BACKGROUND Diabetic foot ulcer (DFU) is one of the leading complications of type-2 diabetes mellitus. It is associated with neuropathy and peripheral arterial disease of the lower limb in patients with diabetes. There are four stages of wound healing, namely hemostasis phase, inflammatory phase, proliferative phase and maturation phase. In the case of DFU, all these stages are disturbed which lead to delay in healing and consequently to lower limb amputation. Conventional dosage forms like tablets, creams, ointments, gels and capsules have been used for the treatment of diabetic foot ulcer for many years. INTRODUCTION In this review, the global prevalence as well as etiopathogenesis related to diabetic foot ulcer have been discussed. The potential role of various synthetic and herbal drugs, as well as their conventional dosage forms in the effective management of DFU have been discussed in detail. METHODS Structured search of bibliographic databases from previously published peer-reviewed research papers was explored and data has been represented in terms of various approaches that are used for the treatment of DFU. RESULTS About 148 papers, including both research and review articles, were included in this review to produce a comprehensive as well as a readily understandable article. A series of herbal and synthetic drugs have been discussed along with their current status of treatment in terms of dose and mechanism of action. CONCLUSION DFU has become one of the most common complications in patients having diabetes for more than ten years. Hence, understanding the root cause and its successful treatment is a big challenge because it depends upon multiple factors such as the judicious selection of drugs as well as proper control of blood sugar level. Most of the drugs that have been used so far either belong to the category of antibiotics, antihyperglycaemic or they have been repositioned. In clinical practice, much focus has been given to dressings that have been used to cover the ulcer. The complete treatment of DFU is still a farfetched dream to be achieved and it is expected that combination therapy of herbal and synthetic drugs with multiple treatment pathways could be able to offer better management of DFU.
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Affiliation(s)
- Ankit Awasthi
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Sachin Kumar Singh
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Bimlesh Kumar
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Monica Gulati
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Rajesh Kumar
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Sheetu Wadhwa
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Rubiya Khursheed
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Leander Corrie
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Arya Kr
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Rajan Kumar
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Pooja Patni
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Jaskiran Kaur
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Sukriti Vishwas
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
| | - Ankit Yadav
- School of Pharmaceutical Sciences, Lovely Professional University Phagwara, 144411, Punjab, India
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Ke W, Rodkey EA, Sampson JM, Skalweit MJ, Sheri A, Pagadala SRR, Nottingham MD, Buynak JD, Bonomo RA, van den Akker F. The importance of the trans-enamine intermediate as a β-lactamase inhibition strategy probed in inhibitor-resistant SHV β-lactamase variants. ChemMedChem 2012; 7:1002-8. [PMID: 22438274 DOI: 10.1002/cmdc.201200006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Indexed: 11/07/2022]
Abstract
The ability of bacteria to express inhibitor-resistant (IR) β-lactamases is stimulating the development of novel inhibitors of these enzymes. The 2'β-glutaroxypenicillinate sulfone, SA2-13, was previously designed to enhance the stabilization of the deacylation-refractory, trans-enamine inhibitory intermediate. To test whether this mode of inhibition can overcome different IR mutations, we determined the binding mode of SA2-13 through X-ray crystallography, obtaining co-crystals of the inhibitor-protein complex by soaking crystals of the IR sulfhydryl variable (SHV) β-lactamase variants S130G and M69V with the inhibitor. The 1.45 Å crystal structure of the S130G SHV:SA2-13 complex reveals that SA2-13 is still able to form the stable trans-enamine intermediate similar to the wild-type complex structure, yet with its carboxyl linker shifted deeper into the active site in the space vacated by the S130G mutation. In contrast, data from crystals of the M69V SHV:SA2-13 complex at 1.3 Å did not reveal clear inhibitor density indicating that this IR variant disfavors the trans-enamine conformation, likely due to a subtle shift in A237.
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Affiliation(s)
- Wei Ke
- Department of Biochemistry, RT500, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
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6
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Frase H, Smith CA, Toth M, Champion MM, Mobashery S, Vakulenko SB. Identification of products of inhibition of GES-2 beta-lactamase by tazobactam by x-ray crystallography and spectrometry. J Biol Chem 2011; 286:14396-409. [PMID: 21345789 PMCID: PMC3077639 DOI: 10.1074/jbc.m110.208744] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2010] [Revised: 01/19/2011] [Indexed: 01/28/2023] Open
Abstract
The GES-2 β-lactamase is a class A carbapenemase, the emergence of which in clinically important bacterial pathogens is a disconcerting development as the enzyme confers resistance to carbapenem antibiotics. Tazobactam is a clinically used inhibitor of class A β-lactamases, which inhibits the GES-2 enzyme effectively, restoring susceptibility to β-lactam antibiotics. We have investigated the details of the mechanism of inhibition of the GES-2 enzyme by tazobactam. By the use of UV spectrometry, mass spectroscopy, and x-ray crystallography, we have documented and identified the involvement of a total of seven distinct GES-2·tazobactam complexes and one product of the hydrolysis of tazobactam that contribute to the inhibition profile. The x-ray structures for the GES-2 enzyme are for both the native (1.45 Å) and the inhibited complex with tazobactam (1.65 Å). This is the first such structure of a carbapenemase in complex with a clinically important β-lactam inhibitor, shedding light on the structural implications for the inhibition process.
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Affiliation(s)
- Hilary Frase
- From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 and
| | - Clyde A. Smith
- the Stanford Synchrotron Radiation Laboratory, Stanford University, Menlo Park, California 94025
| | - Marta Toth
- From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 and
| | - Matthew M. Champion
- From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 and
| | - Shahriar Mobashery
- From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 and
| | - Sergei B. Vakulenko
- From the Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 and
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7
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Abstract
Since the introduction of penicillin, beta-lactam antibiotics have been the antimicrobial agents of choice. Unfortunately, the efficacy of these life-saving antibiotics is significantly threatened by bacterial beta-lactamases. beta-Lactamases are now responsible for resistance to penicillins, extended-spectrum cephalosporins, monobactams, and carbapenems. In order to overcome beta-lactamase-mediated resistance, beta-lactamase inhibitors (clavulanate, sulbactam, and tazobactam) were introduced into clinical practice. These inhibitors greatly enhance the efficacy of their partner beta-lactams (amoxicillin, ampicillin, piperacillin, and ticarcillin) in the treatment of serious Enterobacteriaceae and penicillin-resistant staphylococcal infections. However, selective pressure from excess antibiotic use accelerated the emergence of resistance to beta-lactam-beta-lactamase inhibitor combinations. Furthermore, the prevalence of clinically relevant beta-lactamases from other classes that are resistant to inhibition is rapidly increasing. There is an urgent need for effective inhibitors that can restore the activity of beta-lactams. Here, we review the catalytic mechanisms of each beta-lactamase class. We then discuss approaches for circumventing beta-lactamase-mediated resistance, including properties and characteristics of mechanism-based inactivators. We next highlight the mechanisms of action and salient clinical and microbiological features of beta-lactamase inhibitors. We also emphasize their therapeutic applications. We close by focusing on novel compounds and the chemical features of these agents that may contribute to a "second generation" of inhibitors. The goal for the next 3 decades will be to design inhibitors that will be effective for more than a single class of beta-lactamases.
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Affiliation(s)
- Sarah M. Drawz
- Departments of Pathology, Medicine, Pharmacology, Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, Ohio, Research Service, Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, Ohio
| | - Robert A. Bonomo
- Departments of Pathology, Medicine, Pharmacology, Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, Ohio, Research Service, Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, Ohio
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8
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Simona F, Magistrato A, Dal Peraro M, Cavalli A, Vila AJ, Carloni P. Common mechanistic features among metallo-beta-lactamases: a computational study of Aeromonas hydrophila CphA enzyme. J Biol Chem 2009; 284:28164-28171. [PMID: 19671702 DOI: 10.1074/jbc.m109.049502] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Metallo-beta-lactamases (MbetaLs) constitute an increasingly serious clinical threat by giving rise to beta-lactam antibiotic resistance. They accommodate in their catalytic pocket one or two zinc ions, which are responsible for the hydrolysis of beta-lactams. Recent x-ray studies on a member of the mono-zinc B2 MbetaLs, CphA from Aeromonas hydrophila, have paved the way to mechanistic studies of this important subclass, which is selective for carbapenems. Here we have used hybrid quantum mechanical/molecular mechanical methods to investigate the enzymatic hydrolysis by CphA of the antibiotic biapenem. Our calculations describe the entire reaction and point to a new mechanistic description, which is in agreement with the available experimental evidence. Within our proposal, the zinc ion properly orients the antibiotic while directly activating a second catalytic water molecule for the completion of the hydrolytic cycle. This mechanism provides an explanation for a variety of mutagenesis experiments and points to common functional facets across B2 and B1 MbetaLs.
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Affiliation(s)
- Fabio Simona
- Laboratory of Computational Chemistry and Biochemistry, Department für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
| | - Alessandra Magistrato
- CNR-INFM-Democritos National Simulation Center, via Beirut 4, 34014 Grignano, Trieste, Italy; SISSA, Via Beirut 2-4, 34014 Grignano, Trieste, Italy
| | - Matteo Dal Peraro
- Laboratory for Biomolecular Modeling, Institute of Bioengineering, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne, EPFL, CH-1015 Lausanne, Switzerland
| | - Andrea Cavalli
- Department of Pharmaceutical Sciences, University of Bologna, Via Belmeloro 6, I-40126 Bologna, Italy; Department of Drug Discovery and Development, Italian Institute of Technology, Via Morego 30, I-16163 Genova, Italy
| | - Alejandro J Vila
- Instituto de BiologiaMolecular y Celular de Rosario, Facultad de Bioquímicas y Farmaceuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina
| | - Paolo Carloni
- SISSA, Via Beirut 2-4, 34014 Grignano, Trieste, Italy.
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Li R, Feng D, Feng S. Computational study on decarboxylation mechanism of β-lactamases inhibitors: Clavulanate vs. sulbactam. Chem Phys Lett 2009. [DOI: 10.1016/j.cplett.2009.03.031] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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10
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Pattanaik P, Bethel CR, Hujer AM, Hujer KM, Distler AM, Taracila M, Anderson VE, Fritsche TR, Jones RN, Pagadala SRR, van den Akker F, Buynak JD, Bonomo RA. Strategic design of an effective beta-lactamase inhibitor: LN-1-255, a 6-alkylidene-2'-substituted penicillin sulfone. J Biol Chem 2008; 284:945-53. [PMID: 18955486 DOI: 10.1074/jbc.m806833200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In an effort to devise strategies for overcoming bacterial beta-lactamases, we studied LN-1-255, a 6-alkylidene-2'-substituted penicillin sulfone inhibitor. By possessing a catecholic functionality that resembles a natural bacterial siderophore, LN-1-255 is unique among beta-lactamase inhibitors. LN-1-255 combined with piperacillin was more potent against Escherichia coli DH10B strains bearing bla(SHV) extended-spectrum and inhibitor-resistant beta-lactamases than an equivalent amount of tazobactam and piperacillin. In addition, LN-1-255 significantly enhanced the activity of ceftazidime and cefpirome against extended-spectrum cephalosporin and Sme-1 containing carbapenem-resistant clinical strains. LN-1-255 inhibited SHV-1 and SHV-2 beta-lactamases with nm affinity (K(I) = 110 +/- 10 and 100 +/- 10 nm, respectively). When LN-1-255 inactivated SHV beta-lactamases, a single intermediate was detected by mass spectrometry. The crystal structure of LN-1-255 in complex with SHV-1 was determined at 1.55A resolution. Interestingly, this novel inhibitor forms a bicyclic aromatic intermediate with its carbonyl oxygen pointing out of the oxyanion hole and forming hydrogen bonds with Lys-234 and Ser-130 in the active site. Electron density for the "tail" of LN-1-255 is less ordered and modeled in two conformations. Both conformations have the LN-1-255 carboxyl group interacting with Arg-244, yet the remaining tails of the two conformations diverge. The observed presence of the bicyclic aromatic intermediate with its carbonyl oxygen positioned outside of the oxyanion hole provides a rationale for the stability of this inhibitory intermediate. The 2'-substituted penicillin sulfone, LN-1-255, is proving to be an important lead compound for novel beta-lactamase inhibitor design.
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Affiliation(s)
- Priyaranjan Pattanaik
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA
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11
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Abstract
The partnering of a beta-lactam with a beta-lactamase inhibitor is a highly effective strategy that can be used to combat bacterial resistance to beta-lactam antibiotics mediated by serine beta-lactamases (EC 3.2.5.6). To this end, we tested two novel penem inhibitors against OXA-1, a class D beta-lactamase that is resistant to inactivation by tazobactam. The K(i) of each penem inhibitor for OXA-1 was in the nM range (K(i) of penem 1, 45 +/- 8 nM; K(i) of penem 2, 12 +/- 2 nM). The first-order rate constant for enzyme and inhibitor complex inactivation of penems 1 and 2 for OXA-1 beta-lactamase were 0.13 +/- 0.01 s(-1) and 0.11 +/- 0.01 s(-1), respectively. By using an inhibitor-to-enzyme ratio of 1:1, 100% inactivation was achieved in <or=900 s and the recovery of OXA-1 beta-lactamase activity was not detected at 24 h. Covalent adducts of penems 1 and 2 (changes in molecular masses, +306 +/- 3 and +321 +/- 3 Da, respectively) were identified by electrospray ionization mass spectrometry (ESI-MS). After tryptic digestion of OXA-1 inactivated by penems 1 and 2, ESI-MS and matrix-assisted laser desorption ionization-time-of-flight MS identified the adducts of 306 +/- 3 and 321 +/- 3 Da attached to the peptide containing the active-site Ser67. The base hydrolysis of penem 2, monitored by serial (1)H nuclear magnetic resonance analysis, suggested that penem 2 formed a linear imine species that underwent 7-endo-trig cyclization to ultimately form a cyclic enamine, the 1,4-thiazepine derivative. Susceptibility testing demonstrated that the penem inhibitors at 4 mg/liter effectively restored susceptibility to piperacillin. Penem beta-lactamase inhibitors which demonstrate high affinities and which form long-lived acyl intermediates may prove to be extremely useful against the broad range of inhibitor-resistant serine beta-lactamases present in gram-negative bacteria.
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12
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Totir MA, Cha J, Ishiwata A, Wang B, Sheri A, Anderson VE, Buynak J, Mobashery S, Carey PR. Why clinically used tazobactam and sulbactam are poor inhibitors of OXA-10 beta-lactamase: Raman crystallographic evidence. Biochemistry 2008; 47:4094-101. [PMID: 18324783 DOI: 10.1021/bi702348w] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The clinically used inhibitors tazobactam and sulbactam are effective in the inhibition of activity of class A beta-lactamases, but not for class D beta-lactamases. The two inhibitors exhibit a complex multistep profile for their chemistry of inhibition with class A beta-lactamases. To compare the inhibition profiles for class A and D enzymes, the reactions were investigated within OXA-10 beta-lactamase (a class D enzyme) crystals using a Raman microscope. The favored reaction pathway appears to be distinctly different from that for class A beta-lactamases. In contrast to the case of class A enzymes that favor the formation of a key enamine species, the OXA-10 enzyme forms an alpha,beta-unsaturated acrylate (acid or ester). Quantum mechanical calculations support the likely product as the adduct of Ser115 to the acrylate. Few enamine-like species are formed by sulbactam or tazobactam with this enzyme. Taken together, our results show that the facile conversion of the initial imine, formed upon acylation of the active site Ser67, to the cis- and/or trans-enamine is disfavored. Instead, there is a significant population of the imine that could either experience cross-linking to a second nucleophile (e.g., Ser115) or give rise to the alpha,beta-unsaturated product and permanent inhibition. Alternatively, the imine can undergo hydrolysis to regenerate the catalytically active OXA-10 enzyme. This last process is the dominant one for class D beta-lactamases since the enzyme is not effectively inhibited. In contrast to sulbactam and tazobactam, the reactions between oxacillin or 6alpha-hydroxyisopropylpenicillinate (both substrates) and OXA-10 beta-lactamase appear much less complex. These compounds lead to a single acyl-enzyme species, the presence of which was confirmed by Raman and MALDI-TOF experiments.
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Affiliation(s)
- Monica A Totir
- Departments of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA
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14
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Thomson JM, Distler AM, Bonomo RA. Overcoming Resistance to β-Lactamase Inhibitors: Comparing Sulbactam to Novel Inhibitors against Clavulanate Resistant SHV Enzymes with Substitutions at Ambler Position 244. Biochemistry 2007; 46:11361-8. [PMID: 17848099 DOI: 10.1021/bi700792a] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Amino acid changes at Ambler position R244 in class A TEM and SHV beta-lactamases confer resistance to ampicillin/clavulanate, a beta-lactam/beta-lactamase inhibitor combination used to treat serious infections. To gain a deeper understanding of this resistance phenotype, we investigated the activities of sulbactam and two novel penem beta-lactamase inhibitors with sp2 hybridized C3 carboxylates and bicyclic R1 side chains against a library of SHV beta-lactamase variants at the 244 position. Compared to SHV-1 expressed in Escherichia coli, all 19 R244 variants exhibited increased susceptibility to ampicillin/sulbactam, an important difference compared to ampicillin/clavulanate. Kinetic analyses of SHV-1 and three SHV R244 (-S, -Q, and -L) variants revealed the Ki for sulbactam was significantly elevated for the R244 variants, but the partition ratios, kcat/kinact, were markedly reduced (13 000 --> <or=500). A timed inactivation-mass spectrometry analysis of SHV inhibited by sulbactam showed that SHV-1 beta-lactamase was unmodified at 15 min. A parallel experiment with R244S demonstrated 70 and 88 +/- 3 Da fragments of sulbactam covalently attached to the beta-lactamase. We also observed that the Ki values of penems 1 and 2 were increased for R244 variants compared to those for SHV; however, these inhibitors effectively restored ampicillin susceptibility in vitro. Compared to that of sulbactam, the kcat/kinact values of penems for SHV-1 and R244S were low (<or=2), and unfragmented adducts of each penem were covalently attached to SHV-1 and R244S when studied using the timed inactivation-mass spectrometry method. The R244S mutation affects beta-lactamase inactivators differently, but resistance can be overcome by designing penem inhibitors with strategic chemical properties that improve affinity and impair turnover.
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Affiliation(s)
- Jodi M Thomson
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106, USA
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15
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Padayatti PS, Sheri A, Totir MA, Helfand MS, Carey MP, Anderson VA, Carey PR, Bethel CR, Bonomo RA, Buynak JD, van den Akker F. Rational design of a beta-lactamase inhibitor achieved via stabilization of the trans-enamine intermediate: 1.28 A crystal structure of wt SHV-1 complex with a penam sulfone. J Am Chem Soc 2007; 128:13235-42. [PMID: 17017804 PMCID: PMC2593906 DOI: 10.1021/ja063715w] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
beta-Lactamases are one of the major causes of antibiotic resistance in Gram negative bacteria. The continuing evolution of beta-lactamases that are capable of hydrolyzing our most potent beta-lactams presents a vexing clinical problem, in particular since a number of them are resistant to inhibitors. The efficient inhibition of these enzymes is therefore of great clinical importance. Building upon our previous structural studies that examined tazobactam trapped as a trans-enamine intermediate in a deacylation deficient SHV variant, we designed a novel penam sulfone derivative that forms a more stable trans-enamine intermediate. We report here the 1.28 A resolution crystal structure of wt SHV-1 in complex with a rationally designed penam sulfone, SA2-13. The compound is covalently bound to the active site of wt SHV-1 similar to tazobactam yet forms an additional salt-bridge with K234 and hydrogen bonds with S130 and T235 to stabilize the trans-enamine intermediate. Kinetic measurements show that SA2-13, once reacted with SHV-1 beta-lactamase, is about 10-fold slower at being released from the enzyme compared to tazobactam. Stabilizing the trans-enamine intermediate represents a novel strategy for the rational design of mechanism-based class A beta-lactamase inhibitors.
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Affiliation(s)
- Pius S. Padayatti
- Department of Biochemistry, Case Western Reserve University, Cleveland Ohio 44106
| | - Anjaneyulu Sheri
- Department of Chemistry, Southern Methodist University, Dallas TX 75275-0314
| | - Monica A. Totir
- Department of Chemistry, Case Western Reserve University, Cleveland Ohio 44106
| | - Marion S. Helfand
- Research Division, Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland Ohio 44106
| | - Marianne P. Carey
- Department of Biochemistry, Case Western Reserve University, Cleveland Ohio 44106
| | - Vernon A. Anderson
- Department of Biochemistry, Case Western Reserve University, Cleveland Ohio 44106
| | - Paul R. Carey
- Department of Biochemistry, Case Western Reserve University, Cleveland Ohio 44106
| | - Christopher R. Bethel
- Research Division, Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland Ohio 44106
| | - Robert A. Bonomo
- Research Division, Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland Ohio 44106
- Department of Pharmacology, Case Western Reserve University, Cleveland Ohio 44106
| | - John D. Buynak
- Department of Chemistry, Southern Methodist University, Dallas TX 75275-0314
| | - Focco van den Akker
- Department of Biochemistry, Case Western Reserve University, Cleveland Ohio 44106
- Corresponding author:
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16
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Helfand MS, Taracila MA, Totir MA, Bonomo RA, Buynak JD, van den Akker F, Carey PR. Raman crystallographic studies of the intermediates formed by Ser130Gly SHV, a beta-lactamase that confers resistance to clinical inhibitors. Biochemistry 2007; 46:8689-99. [PMID: 17595114 DOI: 10.1021/bi700581q] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Antibiotic resistance to beta-lactam compounds in Gram-negative bacteria such as Escherichia coli and Klebsiella pneumoniae is often mediated by beta-lactamase enzymes like TEM and SHV. Previously, a limited number of inhibitors have shown efficacy in combating such bacterial drug resistance. However, many Gram-negative pathogens have evolved inhibitor resistant forms of these hydrolytic enzymes. A single point mutation of the active site residue Ser130 to a Gly in either TEM or SHV results in resistance to amoxicillin and clavulanic acid, an important clinical beta-lactam-beta-lactamase inhibitor combination antibiotic. Previous structural and modeling studies of the S130G mutants of TEM and SHV have shown differences in how these two distinct but closely related enzymes compensate for the loss of the Ser130 residue. In the case of S130G SHV, a structure of tazobactam in the active site has suggested that the inhibitor preferentially assumes a cis-enamine intermediate form when the Ser130 hydroxyl is absent. Raman crystallographic studies of S130G SHV inhibited with tazobactam, sulbactam, clavulanic acid, and 2'-glutaroxy penem sulfone (SA2-13) were performed with the aim of identifying the type and amount of intermediate formed with each drug to understand the role of the S130G mutation in formation of the important enamine intermediates. It is demonstrated that with the exception of sulbactam, each compound forms observable trans-enamine intermediates. For S130G reacted with tazobactam, identical steady state levels of enamine are achieved when compared to those of wild-type (WT) or even deacylation deficient forms of the enzyme. With clavulanic acid, slightly smaller amounts of enamine are observed within the first 30 min of the reaction but are not significantly different than those for tazobactam. Thus, the resistance mutation does not substantially affect the amount of trans-enamine formed with clavulanic acid during the critical early time period of inhibition. This finding has important implications in the design of beta-lactamase inhibitors for drug resistant variants like S130G SHV.
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Affiliation(s)
- Marion S Helfand
- Research Service and Infectious Diseases Section, Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, OH 44106, USA.
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17
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Hata M, Fujii Y, Tanaka Y, Ishikawa H, Ishii M, Neya S, Tsuda M, Hoshino T. Substrate deacylation mechanisms of serine-beta-lactamases. Biol Pharm Bull 2007; 29:2151-9. [PMID: 17077507 DOI: 10.1248/bpb.29.2151] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The substrate deacylation mechanisms of serine-beta-lactamases (classes A, C and D) were investigated by theoretical calculations. The deacylation of class A proceeds via four elementary reactions. The rate-determining process is the tetrahedral intermediate (TI) formation and the activation energy is 24.6 kcal/mol at the DFT level. The deacylation does not proceed only by Glu166, which acts as a general base, but Lys73 also participates in the reaction. The C3-carboxyl group of the substrate reduces the barrier height at the TI formation (substrate-assisted catalysis). In the case of class C, the deacylation consists of two elementary processes. The activation energy of the TI formation has been estimated to be 30.5 kcal/mol. Tyr150Oeta is stabilized in the deprotonated state in the acyl-enzyme complex and works as a general base. This situation can exist due to the interaction with two positively charged side chains of lysine (Lys67 and Lys315). The deacylation of class D also consists of two elementary reaction processes. The activation energy of the TI formation is ca. 30 kcal/mol. It is thought that the side chain of Lys70 is deprotonated and acts as a general base. When Lys70 is carbamylated, the activation energy is reduced to less than 20 kcal/mol. This suggests that the high hydrolysis activity of class D with carbamylated Lys70 is due to the reduction of activation energy for deacylation. From these results, it is concluded that the contribution of the lysine residue adjacent to the serine residue is indispensable for the enzymatic reactions by serine-beta-lactamases.
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Affiliation(s)
- Masayuki Hata
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University, Japan.
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18
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Thomson JM, Distler AM, Prati F, Bonomo RA. Probing active site chemistry in SHV beta-lactamase variants at Ambler position 244. Understanding unique properties of inhibitor resistance. J Biol Chem 2006; 281:26734-44. [PMID: 16803899 DOI: 10.1074/jbc.m603222200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inhibitor-resistant class A beta-lactamases are an emerging threat to the use of beta-lactam/beta-lactamase inhibitor combinations (e.g. amoxicillin/clavulanate) in the treatment of serious bacterial infections. In the TEM family of Class A beta-lactamases, single amino acid substitutions at Arg-244 confer resistance to clavulanate inactivation. To understand the amino acid sequence requirements in class A beta-lactamases that confer resistance to clavulanate, we performed site-saturation mutagenesis of Arg-244 in SHV-1, a related class A beta-lactamase found in Klebsiella pneumoniae. Twelve SHV enzymes with amino acid substitutions at Arg-244 resulted in significant increases in minimal inhibitory concentrations to ampicillin/clavulanate when expressed in Escherichia coli. Kinetic analyses of SHV-1, R244S, R244Q, R244L, and R244E beta-lactamases revealed that the main determinant of clavulanate resistance was reduced inhibitor affinity. In contrast to studies in the highly similar TEM enzyme, we observed increases in clavulanate k(inact) for all mutants. Electrospray ionization mass spectrometry of clavulanate inhibited SHV-1 and R244S showed nearly identical mass adducts, arguing against a difference in the inactivation mechanism. Testing a wide range of substrates with C3-4 carboxylates in different stereochemical orientations, we observed impaired affinity for all substrates among inhibitor resistant variants. Lastly, we synthesized two boronic acid transition state analogs that mimic cephalothin and found substitutions at Arg-244 markedly affect both the affinity and kinetics of binding to the chiral, deacylation transition state inhibitor. These data define a role for Arg-244 in substrate and inhibitor binding in the SHV beta-lactamase.
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Affiliation(s)
- Jodi M Thomson
- Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA
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19
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Buynak JD. Understanding the longevity of the beta-lactam antibiotics and of antibiotic/beta-lactamase inhibitor combinations. Biochem Pharmacol 2005; 71:930-40. [PMID: 16359643 DOI: 10.1016/j.bcp.2005.11.012] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2005] [Revised: 11/02/2005] [Accepted: 11/10/2005] [Indexed: 10/25/2022]
Abstract
Microbial resistance necessitates the search for new targets and new antibiotics. However, it is likely that resistance problems will eventually threaten these new products and it may, therefore, be instructive to review the successful employment of beta-lactam antibiotic/beta-lactamase inhibitor combinations to combat penicillin resistance. These combination drugs have proven successful for more than two decades, with inhibitor resistance still being relatively rare. The beta-lactamase inhibitors are mechanism-based irreversible inactivators. The ability of the inhibitors to avoid resistance may be due to the structural similarities between the substrate and inhibitor.
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Affiliation(s)
- John D Buynak
- Department of Chemistry, Southern Methodist University, Dallas, TX 75275-0314, USA.
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20
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Hata M, Tanaka Y, Fujii Y, Neya S, Hoshino T. A Theoretical Study on the Substrate Deacylation Mechanism of Class C β-Lactamase. J Phys Chem B 2005; 109:16153-60. [PMID: 16853052 DOI: 10.1021/jp045403q] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The whole reaction of the deacylation of class C beta-lactamase was investigated by performing quantum chemical calculations under physiological conditions. In this study, the X-ray crystallographic structure of the inhibitor moxalactam-bound class C beta-lactamase (Patera et al. J. Am. Chem. Soc. 2000, 122, 10504-10512.) was utilized and moxalactam was changed into the substrate cefaclor. A model for quantum chemical calculations was constructed using an energy-minimized structure of the substrate-bound enzyme obtained by molecular mechanics calculation, in which the enzyme was soaked in thousands of TIP3P water molecules. It was found that the deacylation reaction consisted of two elementary processes. The first process was formation of a tetrahedral intermediate, which was initiated by the activation of catalytic water by Tyr150, and the second process was detachment of the hydroxylated substrate from the enzyme, which associated with proton transfer from the side chain of Lys67 to Ser64O(gamma). The first process is a rate-determining process, and the activation energy was estimated to be 30.47 kcal/mol from density functional theory calculations considering electron correlation (B3LYP/6-31G**). The side chain of Tyr150 was initially in a deprotonated state and was stably present in the active site of the acyl-enzyme complex, being held by Lys67 and Lys315 cooperatively.
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Affiliation(s)
- Masayuki Hata
- Department of Physical Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba 263-8522, Japan.
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21
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Sulton D, Pagan-Rodriguez D, Zhou X, Liu Y, Hujer AM, Bethel CR, Helfand MS, Thomson JM, Anderson VE, Buynak JD, Ng LM, Bonomo RA. Clavulanic acid inactivation of SHV-1 and the inhibitor-resistant S130G SHV-1 beta-lactamase. Insights into the mechanism of inhibition. J Biol Chem 2005; 280:35528-36. [PMID: 15987690 DOI: 10.1074/jbc.m501251200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Clavulanic acid is a potent mechanism-based inhibitor of TEM-1 and SHV-1beta-lactamases, enzymes that confer resistance to beta-lactams in many gram-negative pathogens. This compound has enjoyed widespread clinical use as part of beta-lactam beta-lactamase inhibitor therapy directed against penicillin-resistant pathogens. Unfortunately, the emergence of clavulanic acid-resistant variants of TEM-1 and SHV-1 beta-lactamase significantly compromise the efficacy of this combination. A single amino acid change at Ambler position Ser130 (Ser --> Gly) results in resistance to inactivation by clavulanate in the SHV-1 and TEM-1beta-lactamases. Herein, we investigated the inactivation of SHV-1 and the inhibitor-resistant S130G variant beta-lactamases by clavulanate. Using liquid chromatography electrospray ionization mass spectrometry, we detected multiple modified proteins when SHV-1 beta-lactamase is inactivated by clavulanate. Matrix-assisted laser desorption ionization-time of flight mass spectrometry was used to study tryptic digests of SHV-1 and S130Gbeta-lactamases (+/- inactivation with clavulanate) and identified peptides modified at the active site Ser70. Ultraviolet (UV) difference spectral studies comparing SHV-1 and S130Gbeta-lactamases inactivated by clavulanate showed that the formation of reaction intermediates with absorption maxima at 227 and 280 nm are diminished and delayed when S130Gbeta-lactamase is inactivated. We conclude that the clavulanic acid inhibition of the S130G beta-lactamase must follow a branch of the normal inactivation pathway. These findings highlight the importance of understanding the intermediates formed in the inactivation process of inhibitor-resistant beta-lactamases and suggest how strategic chemical design can lead to novel ways to inhibit beta-lactamases.
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Affiliation(s)
- Deley Sulton
- Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115, USA
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Fisher JF, Meroueh SO, Mobashery S. Bacterial resistance to beta-lactam antibiotics: compelling opportunism, compelling opportunity. Chem Rev 2005; 105:395-424. [PMID: 15700950 DOI: 10.1021/cr030102i] [Citation(s) in RCA: 676] [Impact Index Per Article: 35.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Jed F Fisher
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
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23
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Georgopapadakou NH. β-Lactamase inhibitors: evolving compounds for evolving resistance targets. Expert Opin Investig Drugs 2005; 13:1307-18. [PMID: 15461559 DOI: 10.1517/13543784.13.10.1307] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The many and diverse beta-lactamases produced by bacteria, particularly by Gram-negative pathogens, are increasingly posing a serious threat to the clinical utility of beta-lactams. First-generation inhibitors (clavulanic acid, sulbactam, tazobactam) focus on Ambler class A enzymes. However, recent structural upgrades of class A beta-lactamases (e.g. TEM, SHV) have extended their spectrum (extended-spectrum beta-lactamases and carbapenemases [Sme, NMC-A, IMI-1]) and have brought about the possibility of beta-lactamase-inhibitor resistance. Furthermore, the mobilisation and spread of originally chromosomal class C enzymes (CMY, MIR), the growing clinical importance of class B enzymes (IMP, VIM), the emergence of inhibitor-resistant, broad spectrum class D (OXA) enzymes and the co-existence of different classes of beta-lactamases in the same pathogen have spurred research toward universal inhibitors. A complicating issue is target accessibility in Gram-negative bacteria, particularly in Enterobacter, Acinetobacter, Pseudomonas, Stenotrophomonas and other organisms, which is necessary in order for the inhibitor to synergise with vulnerable beta-lactam antibiotics. Several new, broad-spectrum inhibitors have emerged: cephem sulfones and oxapenems are upgrades of penam sulfones and oxapenams, respectively, with cephem sulfones possibly extending their inhibition to class B metallo-enzymes; and boronates and phosphonates are designed de novo, based on common structural and mechanistic features of serine beta-lactamases.
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