I03-Macromolecular Crystallography
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Open Access
Abstract: Acinetobacter baumannii is a gram-negative bacterial pathogen that causes challenging nosocomial infections. β-lactam targeting of penicillin-binding protein (PBP)–mediated cell wall peptidoglycan (PG) formation is a well-established antimicrobial strategy. Exposure to carbapenems or zinc (Zn)-deprived growth conditions leads to a rod-to-sphere morphological transition in A. baumannii, an effect resembling that caused by deficiency in the RodA–PBP2 PG synthesis complex required for cell wall elongation. While it is recognized that carbapenems preferentially acylate PBP2 in A. baumannii and therefore block the transpeptidase function of the RodA–PBP2 system, the molecular details underpinning cell wall elongation inhibition upon Zn starvation remain undefined. Here, we report the X-ray crystal structure of A. baumannii PBP2, revealing an unexpected Zn coordination site in the transpeptidase domain required for protein stability. Mutations in the Zn-binding site of PBP2 cause a loss of bacterial rod shape and increase susceptibility to β-lactams, therefore providing a direct rationale for cell wall shape maintenance and Zn homeostasis in A. baumannii. Furthermore, the Zn-coordinating residues are conserved in various β- and γ-proteobacterial PBP2 orthologs, consistent with a widespread Zn-binding requirement for function that has been previously unknown. Due to the emergence of resistance to virtually all marketed antibiotic classes, alternative or complementary antimicrobial strategies need to be explored. These findings offer a perspective for dual inhibition of Zn-dependent PG synthases and metallo-β-lactamases by metal chelating agents, considered the most sought-after adjuvants to restore β-lactam potency against gram-negative bacteria.
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Feb 2023
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I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
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Hector
Newman
,
Alen
Krajnc
,
Domenico
Bellini
,
Charles J.
Eyermann
,
Grant A.
Boyle
,
Neil
Paterson
,
Katherine E.
Mcauley
,
Robert
Lesniak
,
Mukesh
Gangar
,
Frank
Von Delft
,
Jurgen
Brem
,
Kelly
Chibale
,
Christopher J.
Schofield
,
Christopher G.
Dowson
Diamond Proposal Number(s):
[17884]
Open Access
Abstract: The effectiveness of β-lactam antibiotics is increasingly compromised by β-lactamases. Boron-containing inhibitors are potent serine-β-lactamase inhibitors, but the interactions of boron-based compounds with the penicillin-binding protein (PBP) β-lactam targets have not been extensively studied. We used high-throughput X-ray crystallography to explore reactions of a boron-containing fragment set with the Pseudomonas aeruginosa PBP3 (PaPBP3). Multiple crystal structures reveal that boronic acids react with PBPs to give tricovalently linked complexes bonded to Ser294, Ser349, and Lys484 of PaPBP3; benzoxaboroles react with PaPBP3 via reaction with two nucleophilic serines (Ser294 and Ser349) to give dicovalently linked complexes; and vaborbactam reacts to give a monocovalently linked complex. Modifications of the benzoxaborole scaffold resulted in a moderately potent inhibition of PaPBP3, though no antibacterial activity was observed. Overall, the results further evidence the potential for the development of new classes of boron-based antibiotics, which are not compromised by β-lactamase-driven resistance.
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Jul 2021
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I02-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
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Abstract: Branched Lipid II, required for the formation of indirectly crosslinked peptidoglycan, is generated by MurM, a protein essential for high-level penicillin resistance in the human pathogen Streptococcus pneumoniae. We have solved the X-ray crystal structure of Staphylococcus aureus FemX, an isofunctional homolog, and have used this as a template to generate a MurM homology model. Using this model, we perform molecular docking and molecular dynamics to examine the interaction of MurM with the phospholipid bilayer and the membrane-embedded Lipid II substrate. Our model suggests that MurM is associated with the major membrane phospholipid cardiolipin, and experimental evidence confirms that the activity of MurM is enhanced by this phospholipid and inhibited by its direct precursor phosphatidylglycerol. The spatial association of pneumococcal membrane phospholipids and their impact on MurM activity may therefore be critical to the final architecture of peptidoglycan and the expression of clinically relevant penicillin resistance in this pathogen.
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Mar 2021
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I03-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Sarah L.
Kidd
,
Elaine
Fowler
,
Till
Reinhardt
,
Thomas
Compton
,
Natalia
Mateu
,
Hector
Newman
,
Dom
Bellini
,
Romain
Talon
,
Joseph
Mcloughlin
,
Tobias
Krojer
,
Anthony
Aimon
,
Anthony
Bradley
,
Michael
Fairhead
,
Paul
Brear
,
Laura
Diaz-Saez
,
Katherine
Mcauley
,
Hannah F.
Sore
,
Andrew
Madin
,
Daniel H.
O'Donovan
,
Kilian
Huber
,
Marko
Hyvonen
,
Frank
Von Delft
,
Christopher G.
Dowson
,
David R.
Spring
Diamond Proposal Number(s):
[18145, 15649, 14303, 14493]
Open Access
Abstract: Organic synthesis underpins the evolution of weak fragment hits into potent lead compounds. Deficiencies within current screening collections often result in the requirement of significant synthetic investment to enable multidirectional fragment growth, limiting the efficiency of the hit evolution process. Diversity-oriented synthesis (DOS)-derived fragment libraries are constructed in an efficient and modular fashion and thus are well-suited to address this challenge. To demonstrate the effective nature of such libraries within fragment-based drug discovery, we herein describe the screening of a 40-member DOS library against three functionally distinct biological targets using X-Ray crystallography. Firstly, we demonstrate the importance for diversity in aiding hit identification with four fragment binders resulting from these efforts. Moreover, we also exemplify the ability to readily access a library of analogues from cheap commercially available materials, which ultimately enabled the exploration of a minimum of four synthetic vectors from each molecule. In total, 10–14 analogues of each hit were rapidly accessed in three to six synthetic steps. Thus, we showcase how DOS-derived fragment libraries enable efficient hit derivatisation and can be utilised to remove the synthetic limitations encountered in early stage fragment-based drug discovery.
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May 2020
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Ricky
Cain
,
Ramya
Salimraj
,
Avinash
Punekar
,
Dom
Belini
,
Colin W. G.
Fishwick
,
Lloyd
Czaplewski
,
David Jan
Scott
,
Gemma
Harris
,
Christopher G.
Dowson
,
Adrian J.
Lloyd
,
David I.
Roper
Diamond Proposal Number(s):
[14692]
Abstract: Aminoacyl-tRNA synthetases are ubiquitous and essential enzymes for protein synthesis and also a variety of other metabolic processes, especially in bacterial species. Bacterial aminoacyl-tRNA synthetases represent attractive and validated targets for antimicrobial drug discovery if issues of prokaryotic versus eukaryotic selectivity and antibiotic resistance generation can be addressed. We have determined high resolution X-ray crystal structures of the Escherichia coli and Staphylococcus aureus seryl-tRNA synthetases in complex with aminoacyl adenylate analogues and applied a structure-based drug discovery approach to explore and identify a series of small molecule inhibitors that selectively inhibit bacterial seryl-tRNA synthetases with greater than two orders of magnitude compared to their human homologue, demonstrating a route to selective chemical inhibition of these bacterial targets.
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Oct 2019
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Abstract: Even with the emergence of antibiotic resistance, penicillin and the wider family of beta-lactams have remained the single most important family of antibiotics. The periasmic/extracytoplasmic targets of penicillin are a family of enzymes with a highly conserved catalytic activity involved in the final stage of bacterial cell wall (peptidoglycan, PG) biosynthesis. Named after their ability to bind penicillin, rather than their catalytic activity these key targets are called penicillin-binding proteins (PBPs).Resistance is predominantly mediated by reducing the target drug concentration via beta-lactamases, however, naturally transformable bacteria have also acquired target mediated resistance by inter-species recombination. Here we focus on structural based interpretations of amino acid alterations associated with the emergence of resistance within clinical isolates and include new PBP3 structures along with new, and improved, PBP-beta-lactam co-structures.
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Jul 2019
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I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
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Efrat
Resnick
,
Anthony
Bradley
,
Jinrui
Gan
,
Alice
Douangamath
,
Tobias
Krojer
,
Ritika
Sethi
,
Paul P.
Geurink
,
Anthony
Aimon
,
Gabriel
Amitai
,
Dom
Bellini
,
James
Bennett
,
Michael
Fairhead
,
Oleg
Fedorov
,
Ronen
Gabizon
,
Jin
Gan
,
Jingxu
Guo
,
Alexander
Plotnikov
,
Nava
Reznik
,
Gian Filippo
Ruda
,
Laura
Diaz-Saez
,
Verena M.
Straub
,
Tamas
Szommer
,
Srikannathasan
Velupillai
,
Daniel
Zaidman
,
Yanling
Zhang
,
Alun R.
Coker
,
Christopher G.
Dowson
,
Haim
Barr
,
Chu
Wang
,
Kilian V. M.
Huber
,
Paul E.
Brennan
,
Huib
Ovaa
,
Frank
Von Delft
,
Nir
London
Abstract: Covalent probes can display unmatched potency, selectivity and duration of action; however, their discovery is challenging. In principle, fragments that can irreversibly bind their target can overcome the low affinity that limits reversible fragment screening, but such electrophilic fragments were considered non-selective and were rarely screened. We hypothesized that mild electrophiles might overcome the selectivity challenge and constructed a library of 993 mildly electrophilic fragments. We characterized this library by a new high-throughput thiol-reactivity assay and screened them against ten cysteine-containing proteins. Highly reactive and promiscuous fragments were rare and could be easily eliminated. By contrast, we found hits for most targets. Combining our approach with high-throughput crystallography allowed rapid progression to potent and selective probes for two enzymes, the deubiquitinase OTUB2 and the pyrophosphatase NUDT7. No inhibitors were previously known for either. This study highlights the potential of electrophile-fragment screening as a practical and efficient tool for covalent-ligand discovery.
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May 2019
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I04-Macromolecular Crystallography
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Sarah
Batson
,
Cesira
De Chiara
,
Vita
Majce
,
Adrian J.
Lloyd
,
Stanislav
Gobec
,
Dean
Rea
,
Vilmos
Fulop
,
Christopher
Thoroughgood
,
Katie J.
Simmons
,
Christopher G.
Dowson
,
Colin W. G.
Fishwick
,
Luiz Pedro S.
De Carvalho
,
David I.
Roper
Open Access
Abstract: D-cycloserine is an antibiotic which targets sequential bacterial cell wall peptidoglycan biosynthesis enzymes: alanine racemase and D-alanine:D-alanine ligase. By a combination of structural, chemical and mechanistic studies here we show that the inhibition of D-alanine:D-alanine ligase by the antibiotic D-cycloserine proceeds via a distinct phosphorylated form of the drug. This mechanistic insight reveals a bimodal mechanism of action for a single antibiotic on different enzyme targets and has significance for the design of future inhibitor molecules based on this chemical structure.
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Dec 2017
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I02-Macromolecular Crystallography
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Karen M.
Ruane
,
Adrian J.
Lloyd
,
Vilmos
Fulop
,
Christopher G.
Dowson
,
Helene
Barreteau
,
Audrey
Boniface
,
Sebastien
Dementin
,
Didier
Blanot
,
Dominique
Mengin-Lecreulx
,
Stanislav
Gobec
,
Andrea
Dessen
,
David I.
Roper
Diamond Proposal Number(s):
[8359]
Open Access
Abstract: Formation of the peptidoglycan stem pentapeptide requires the insertion of both l and d amino acids by the ATP-dependent ligase enzymes MurC, -D, -E, and -F. The stereochemical control of the third position amino acid in the pentapeptide is crucial to maintain the fidelity of later biosynthetic steps contributing to cell morphology, antibiotic resistance, and pathogenesis. Here we determined the x-ray crystal structure of Staphylococcus aureus MurE UDP-N-acetylmuramoyl-l-alanyl-d-glutamate:meso-2,6-diaminopimelate ligase (MurE) (E.C. 6.3.2.7) at 1.8 Å resolution in the presence of ADP and the reaction product, UDP-MurNAc-l-Ala-?-d-Glu-l-Lys. This structure provides for the first time a molecular understanding of how this Gram-positive enzyme discriminates between l-lysine and d,l-diaminopimelic acid, the predominant amino acid that replaces l-lysine in Gram-negative peptidoglycan. Despite the presence of a consensus sequence previously implicated in the selection of the third position residue in the stem pentapeptide in S. aureus MurE, the structure shows that only part of this sequence is involved in the selection of l-lysine. Instead, other parts of the protein contribute substrate-selecting residues, resulting in a lysine-binding pocket based on charge characteristics. Despite the absolute specificity for l-lysine, S. aureus MurE binds this substrate relatively poorly. In vivo analysis and metabolomic data reveal that this is compensated for by high cytoplasmic l-lysine concentrations. Therefore, both metabolic and structural constraints maintain the structural integrity of the staphylococcal peptidoglycan. This study provides a novel focus for S. aureus-directed antimicrobials based on dual targeting of essential amino acid biogenesis and its linkage to cell wall assembly.
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Sep 2013
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