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D J Payne

Publications and source records attributed to D J Payne.

At least 37 records · Page 2Linked to original sources
PubMed1999

Molecular basis for triclosan activity involves a flipping loop in the active site.

The crystal structure of the Escherichia coli enoyl reductase-NAD+-triclosan complex has been determined at 2.5 A resolution. The Ile192-Ser198 loop is either disordered or in an open conformation in the previously reported structures of the enzyme. This loop adopts a closed conformation in our structure, forming van der Waals interactions with the inhibitor and hydrogen bonds with the bound NAD+ cofactor. The opening and closing of this flipping loop is likely an important factor in substrate or ligand recognition. The closed conformation of the loop appears to be a critical feature for the enhanced binding potency of triclosan, and a key component in future structure-based inhibitor design.

Amino Acid Sequence↗
PubMed1999

Ultrashort laser pulse bioeffects and safety.

Recent studies of retinal damage due to ultrashort laser pulses have shown that less energy is required for retinal damage for pulses shorter than 1 ns than that for longer pulses. It has also been shown that more energy is required for near-infrared (NIR) wavelengths than in the visible because the light focuses behind the retina, requiring more energy to produce a damaging fluence on the retina. We review the progress made in determining the trends in retinal damage from laser pulses of 1 ns to 100 fs in the visible and NIR wavelength regimes. We have determined the most likely damage mechanism(s) operative in this pulse width regime.

Animals↗
PubMed1998

Crystal structure of the zinc-dependent beta-lactamase from Bacillus cereus at 1.9 A resolution: binuclear active site with features of a mononuclear enzyme.

The structure of the zinc-dependent beta-lactamase II from Bacillus cereus has been determined at 1.9 A resolution in a crystal form with two molecules in the asymmetric unit and 400 waters (space group P3121; Rcryst = 20.8%). The active site contains two zinc ions: Zn1 is tightly coordinated by His86, His88, and His149, while Zn2 is loosely coordinated by Asp90, Cys168, and His210. A water molecule (W1) lies between the two zinc ions but is significantly closer to Zn1 and at a distance of only 1.9 A is effectively a hydroxide moiety and a potential, preactivated nucleophile. In fact, Asp90 bridges W1 to Zn2, and its location is thus distinct from that of the bridging water molecules in the binuclear zinc peptidases or other binuclear zinc hydrolases. Modeling of penicillin, cephalosporin, and carbapenem binding shows that all are readily accommodated within the shallow active site cleft of the enzyme, and the Zn1-bound hydroxide is ideally located for nucleophilic attack at the beta-lactam carbonyl. This enzyme also functions with only one zinc ion present. The Zn1-Zn2 distances differ in the two independent molecules in the crystal (3.9 and 4.4 A), yet the Zn1-W1 distances are both 1.9 A, arguing against involvement of Zn2 in W1 activation. The role of Zn2 is unclear, but the B. cereus enzyme may be an evolutionary intermediate between the mono- and bizinc metallo-beta-lactamases. The broad specificity of this enzyme, together with the increasing prevalence of zinc-dependent metallo-beta-lactamases, poses a real clinical threat, and this structure provides a basis for understanding its mechanism and designing inhibitors.

Bacillus cereus↗
PubMed1998

Nucleotide and amino acid sequences of the metallo-beta-lactamase, ImiS, from Aeromonas veronii bv. sobria.

The Aeromonas veronii bv. sobria metallo-beta-lactamase gene, imiS, was cloned. The imiS open reading frame extends for 762 bp and encodes a protein of 254 amino acids with a secreted modified protein of 227 amino acids and a predicted pI of 8.1. To confirm the predicted sequence, purified ImiS was digested and the resulting peptides were identified, yielding an identical sequence for ImiS, with 98% identity to CphA. Both possessed the putative active-site sequence Asn-Tyr-His-Thr-Asp at positions 88 to 92, which is unique to the Aeromonas metallo-beta-lactamases.

Aeromonas↗
PubMed1997

Inhibition of metallo-beta-lactamases by a series of thiol ester derivatives of mercaptophenylacetic acid.

A series of mercaptophenylacetic acid thiol esters bearing a phenyl substituent adjacent to the carboxylic acid function has been shown to be inhibitors of metallo-beta-lactamases. The inhibition of the Bacteroides fragilis CfiA and Bacillus cereus II metallo-beta-lactamases was Zn2- dependent, greater inhibition being observed at 1 microM ZnSO4 than at 100 microM ZnSO4. Despite this Zn2+ dependency, isothermal titration calorimetry studies illustrated that representative compounds had no detectable affinity for Zn2+ (K > 1 mM). This indicates that their mode of inhibition was not by chelation of the active site Zn2+. Greatest potency was observed against the Stenotrophomonas maltophilia L1 metallo-beta-lactamase with I50 values of between < 1.95 microM and 6 microM and SB-217843 exhibited a similar level of inhibition of this enzyme at 1 and 100 microM Zn2+ (I50 values 5 and 6 microM, respectively). Inhibition of B. cereus II metallo-beta-lactamase by SB-218018 and SB-217782 was competitive with Ki values of 185 microM and 1500 microM, respectively. Therefore, these compounds are specific inhibitors of metallo-beta-lactamases and provide further probes of the active sites of these enzymes.

Bacillus cereus↗
PubMed1997

Inhibition of metallo-beta-lactamases by a series of mercaptoacetic acid thiol ester derivatives.

A series of mercaptoacetic acid thiol esters have been identified as metallo-beta-lactamase inhibitors. Electrospray mass spectrometry (ESMS) has shown that irreversible inhibition of the Bacillus cereus II metallo-beta-lactamase by SB214751, SB214752, and SB213079 was concomitant with a 90-Da increase in mass of the enzyme. Tryptic digestion of the B. cereus II inhibited with SB214751 illustrated that the peptide fragment, containing the only cysteine of the enzyme, had undergone a mass increment of 90 Da. It was further demonstrated that B. cereus II hydrolyzed this type of compound across the thiol ester bond to yield mercaptoacetic acid. Mercaptoacetic acid is the only molecular fragment common to SB214751, SB214752, and SB213079, and free mercaptoacetic acid does not bind covalently to B. cereus II. Therefore, it is concluded that these compounds inhibit B. cereus II by the mechanism-based delivery of mercaptoacetic acid, forming a disulfide linkage with the active sites cysteine (predicted mass shift = +90 Da) under the aerobic conditions of the assay. The different thiol esters examined had a broad range of potencies against the metallo-beta-lactamases tested. For example SB214751, SB214752, and SB213079 all had 50% inhibitory concentrations of < 10 and > 1,000 microM for the Stenotrophomonas maltophilia L-1 and Bacteroides fragilis CfiA enzymes, respectively. SB216968 was particularly active against the Aeromonas hydrophila CphA metallo-beta-lactamase and was found to be an uncompetitive inhibitor of this enzyme (Ki = 3.9 microM), whereas it exhibited irreversible inhibition of the L-1 enzyme. These observations with this series of compounds have revealed subtle differences between the active sites of different metallo-beta-lactamases. Finally, a novel application for isothermal titration calorimetry for assessing the zinc chelating activity of candidate inhibitors is also presented.

Aeromonas hydrophila↗
PubMed1996

Phosphonamidate analogues of dipeptides with carboxypeptidase A and beta-lactamase-inhibitory activity: elucidation of the mechanism of beta-lactamase inhibition by electrospray mass spectrometry.

A series of phosphonamidate compounds with different P1' amino acid residues have been shown to be irreversible inactivators of the serine beta-lactamase from Enterobacter cloacae P99. The efficiency of inhibition (based on k2/K values) of P99 by these derivatives, ordered in decreasing potency, is: beta-phenyl-beta-Ala > L-Phe > beta-Ala > Gly > D-Phe > D-Pro > D-thiazolidine. The D- and L-Phe compounds also inhibit carboxypeptidase A. The proline and thiazolidine derivatives were phosphonamidate methyl esters, whereas the others were salts of diacids. Electrospray mass spectrometry showed that equimolar mixtures of the P99 enzyme with each of the following derivatives, Gly, D-Phe, L-Phe, beta-Ala and beta-phenyl-beta-Ala, effected efficient adduct formation (70-95% of enzyme modified), illustrating the particularly active nature of some of these compounds. All the primary amino acid derivatives gave a similar mass increment, which suggests the displacement of the variable P1' part of the molecule. This observation provides evidence that the compounds phosphonylate the active-site serine, with the phosphonamidate bond as the scissile bond and the amino acid as the leaving group. The thiazolidine derivative (phosphonamidate methyl ester) also appeared to work by the same mechanism. The comparable proline derivatives caused lower than expected mass shifts of 227-229, and therefore it is proposed that with these compounds both the amino acid and the phosphonamidate ester methoxy group were displaced at the phosphorus atom during the inhibition process. Therefore, electrospray mass spectrometry has provided both a measure of potency and a rationale for the mechanism of inhibition of P99 by these compounds.

Carboxypeptidases↗
PubMed1996

Production of metal dependent beta-lactamases by clinical strains of Bacteroides fragilis isolated before 1987.

Five imipenem resistant clinical isolates of Bacteroides fragilis isolated before 1987, were examined to determine if they produced metallo-beta-lactamases. The beta-lactamases produced by the clinical isolates all focused as doublet bands at pl 4.8/4.9, characteristic of the B. fragilis CfiA type metallo-beta-lactamase. Each enzyme had a similar substrate profile and were inhibited by EDTA and activated with zinc sulphate. The sequence of the metallo-beta-lactamase gene from B. fragilis ED262 was determined and confirmed to be a CfiA type beta-lactamase. Consequently, the five isolates examined probably produce a CfiA type beta-lactamase, suggesting that metallo-beta-lactamases were present before the widespread use of carbapenems.

Bacteroides fragilis↗
PubMed1995

A clinical isolate of Aeromonas sobria with three chromosomally mediated inducible beta-lactamases: a cephalosporinase, a penicillinase and a third enzyme, displaying carbapenemase activity.

Hydrolytic profiles of Aeromonas sobria 163a, non-induced and induced, and of a derepressed mutant 163a-M, indicate that this strain has inducible beta-lactamases with activities against cephalosporins, penicillins and carbapenems. Three enzymes were identified and two of the beta-lactamase genes, ampS, encoding a penicillinase and cepS, encoding a cephalosporinase, were cloned into Escherichia coli, permitting analysis of the individual enzymes. Isoelectric focusing (IEF) analysis using inhibition profiles with EDTA and BRL 42715, confirmed AmpS (pI 7.9) and CepS (7.0) to be serine beta-lactamases. A third beta-lactamase displaying hydrolytic activity against the carbapenems was inhibited by EDTA. The carbapenemase had a pI of 9.3 and was detected on IEF gels by overlaying the gel with agarose containing imipenem and the chromogenic pH indicator, bromothymol blue. Co-inducibility and the recovery of a derepressed mutant in which all three enzymes were produced at high levels indicate that this isolate of A. sobria has three co-ordinately controlled beta-lactamase genes.

Aeromonas↗
PubMed1994

Kinetic and physical studies of beta-lactamase inhibition by a novel penem, BRL 42715.

The interactions of Staphylococcus aureus, Bacillus cereus I, TEM, Klebsiella pneumoniae K1 and Enterobacter cloacae P99 beta-lactamases with the novel penem inhibitor BRL 42715 were investigated kinetically and, in some cases, by electrospray mass spectrometry (e.s.m.s.). All the beta-lactamases were rapidly inactivated by BRL 42715, with second-order rate constants ranging from 0.17 to 6.4 microM-1.s-1. The initial stoichiometry of beta-lactamase inhibition was essentially 1:1, with the exception of the K1 enzyme. In this instance about 20 molecules of BRL 42715 were hydrolysed before the enzyme was completely inhibited. Inhibited beta-lactamases did not readily regain activity in the absence of BRL 42715, the half-lives for regeneration of free enzyme ranging from 5 min for the K1 beta-lactamase to over 2 days for the staphylococcal enzyme. Recovery of activity was incomplete for TEM-1, K1 and P99 beta-lactamases, suggesting partitioning of the inhibited enzymes to give a permanently (or at least very stable) inactivated species. Examination of the interactions of the penem with TEM, B. cereus I and P99 beta-lactamases by e.s.m.s. also showed rapid and stoichiometric binding of the inhibitor. In all cases a mass increase of 264 Da over the native enzyme was observed, corresponding to the molecular mass of BRL 42715, showing that no fragmentation of the penem occurred on reaction with the beta-lactamases.

Anti-Bacterial Agents↗
PubMed1994

beta-Lactamase ragged ends detected by electrospray mass spectrometry correlates poorly with multiple banding on isoelectric focusing.

Purified preparations of TEM-2, P99, Bacillus cereus I and B. cereus II beta-lactamases were examined by electrospray (ES) mass spectrometry. The ES mass spectra of the B. cereus enzymes revealed the presence of four to five components of different mass, corresponding to the loss of different numbers of N-terminal amino acids (ragged ends). The ES mass spectra of both TEM-2 and P99 consisted of a single component with no evidence of ragged ends. All four beta-lactamase preparations were visualized on isoelectric focusing (IEF) gels stained with nitrocefin to investigate a possible correlation between IEF patterns and ragged ends. Multiple banding patterns were seen with each beta-lactamase preparation. Although these may correlate with the presence of ragged ends in the two B. cereus preparations, the satellite bands seen with P99 and TEM-2 were not associated with differences detected by ES mass spectrometry. In this study we have shown for the first time that beta-lactamase satellite bands seen on IEF are not always associated with ragged ends. Furthermore, we have illustrated the use of ES mass spectrometry to characterize the extent of ragged end formation in protein samples. This is of particular significance if the sample is required for detailed biochemical or crystallography experiments.

Isoelectric Focusing↗
PubMed1994

Bacterial resistance mechanisms as therapeutic targets.

In the 50 years since antimicrobial agents were first introduced, bacteria have acquired a wide variety of mechanisms which have enabled them to resist the effects of these drugs. One way of overcoming this problem is to administer an antibiotic with an agent which counteracts the mechanism of resistance to that antibiotic; an example of such an approach which has already been successfully implemented is the combination of a beta-lactam antibiotic with a beta-lactamase inhibitor. This review describes antibiotic resistance mechanisms which might lend themselves to an inhibitor approach and the potential therapeutic applications of such a strategy.

Bacteria↗
PubMed1994

Comparative activities of clavulanic acid, sulbactam, and tazobactam against clinically important beta-lactamases.

Clavulanic acid, sulbactam, and tazobactam are inhibitors of a variety of plasmid-mediated beta-lactamases. However, inhibition data for these three inhibitors with a wide range of different plasmid-mediated beta-lactamases have not yet been compared under the same experimental conditions. A number of groups have inferred that clavulanic acid inhibits extended-spectrum TEM and SHV beta-lactamases, but inhibition data have rarely been published. In this study, the 50% inhibitory concentrations of these three beta-lactamase inhibitors for 35 plasmid-mediated beta-lactamases have been determined. Of these 35 beta-lactamases, 20 were extended-spectrum TEM- or SHV-derived beta-lactamases. The other 15 enzymes were conventional-spectrum beta-lactamases such as TEM-1 and SHV-1. Clavulanic acid was a more potent inhibitor than sulbactam for 32 of the 35 plasmid-mediated beta-lactamases tested. In particular, clavulanic acid was 60 and 580 times more potent than sulbactam against TEM-1 and SHV-1, respectively, currently the two most clinically prevalent gram-negative plasmid-mediated beta-lactamases. Statistical analysis of the data of the 50% inhibitory concentrations showed that clavulanic acid was 20 times more active overall than sulbactam against the conventional-spectrum enzymes. In addition, clavulanic acid was 14 times more potent than sulbactam at inhibiting the extended-spectrum enzymes. Tazobactam also showed significantly greater activity than sulbactam against the two groups of beta-lactamases. There were no significant differences between the overall activities of tazobactam and clavulanic acid against the extended-spectrum TEM and SHV enzymes and conventional-spectrum enzymes, although differences in their inhibition profiles were observed.

Bacteria↗
PubMed1994

Rapid identification of metallo- and serine beta-lactamases.

Simple methods to detect, identify, and differentiate metallo- and serine beta-lactamases were developed and used to differentiate enzymes produced by 17 clinical isolates of Xanthomonas maltophilia. All isolates exhibited beta-lactamase activity, and in 16 strains this was induced by imipenem. All but one isolate hydrolyzed imipenem (and meropenem), and in all cases this activity was inhibited by 1 mM EDTA. The metallo- and serine beta-lactamases in the cell extracts were distinguished on isoelectric focusing (IEF) gels by using the following procedures. (i) Cell lysates were preincubated with 83 mM EDTA prior to IEF and subsequent visualization with nitrocefin, and (ii) after IEF, the gels were overlaid with either 1 mM zinc sulfate or 100 microM BRL 42715 before staining with nitrocefin. Bands of beta-lactamase activity which were removed by BRL 42715 but unaffected by EDTA or zinc sulfate were categorized as serine beta-lactamases. Bands which were unaffected by BRL 42715 but inhibited by EDTA or enhanced by zinc sulfate were classified as metallo-beta-lactamases. By using this approach, seven metallo-beta-lactamases were differentiated with pI values of 4.8 (two strains), 5.5 (four strains), 5.7 (one strain), 6.0 (one strain), 6.4 (four strains), 6.6 (one strain), and 6.8 (three strains). The metallo-beta-lactamase band with a pI of 6.4 aligned with the recently characterized metallo-beta-lactamase from X. maltophilia 511. Heterogeneity was also observed for the serine beta-lactamases: 14 isolates elaborated serine beta-lactamase activity which focused with major bands with at least eight different pIs. The remaining three strains produced serine beta-lactamases which focused with five distinct bands with pIs of 6.4, 6.2, 5.7, 5.5, and 5.2. We conclude that X. maltophilia produces many types of metallo- and serine beta-lactamases distinguishable by these new methods and that the previously reported L-1 and L-2 enzymes are not solely representative of the beta-lactamases produced by this species.

Anti-Bacterial Agents↗