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Conformational changes in the extracellular beta-lactamase I from Bacillus cereus 569/H/9.

ABSTRACT: 1. The thermal denaturation and precipitation of beta-lactamase I from Bacillus cereus 569/H/9 at 60 degrees C are reversible, a soluble and almost fully active enzyme being obtained after solution of the precipitate in 5m-guanidinium chloride or 8m-urea and subsequent removal of the denaturing agent. 2. Inactivation of beta-lactamase I occurs rapidly between 50 degrees and 55 degrees C and is shown by circular-dichroism spectra to be accompanied by an extensive conformational change. 3. A change to a different conformation occurs in 6m-urea. This change is also reversible; refolding with almost complete recovery of enzymic activity occurs within 5min of dilution of the denaturing agent. 4. Inactivation of beta-lactamase I at pH3.0 and 11.0 is also associated with conformational changes, since a proportion of the lost activity is recovered within 5min of adjustment of the pH to 7.0.

SUBMITTER: Davies RB

PROVIDER: S-EPMC1168361 | biostudies-other | 1974 Oct

REPOSITORIES: biostudies-other

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Comparison of beta-lactamase II from Bacillus cereus 569/H/9 with a beta-lactamase from Bacillus cereus 5/B/6.

Project description:A mutant of Bacillus cereus 5/B, strain 5/B/6, produces a beta-lactamase II-like enzyme but no beta-lactamase I. Beta-lactamases II and II 5/B/6 appear to show a high degree of homology, but there are significant differences in their enzymic properties.

| S-EPMC1165233 | biostudies-other

The partial amino acid sequence of the extracellular beta-lactamase I of Bacillus cereus 569/H.

Project description:The chemical structure of the extracellular beta-lactamase I of Bacillus cereus 569/H was investigated. Three electrophoretically homogenous charge variants of this enzyme were isolated and amino acid analysis of each revealed no significant differences. However, a degree of N-terminal heterogeneity was found by direct end-group modification of the protein and also on alignment of peptides from tryptic and chymotryptic digestion. The N-terminal heterogeneity observed was great enough to explain the production of the beta-lactamase I isoenzymes which are probably produced by postsynthesis modification of a single gene product. Over 80% of the amino acid sequence of beta-lactamase I was determined by the detailed analysis of peptides derived from tryptic, chymotryptic and thermolytic digests. Five polypeptide fragments were constructed from these data and aligned by comparison with the known amino acid sequences of the penicillinases produced by Bacillus licheniformis and Staphylococcus aureus (Ambler & Meadway, 1969). About 60% of the proposed sequence was identical with that of B. licheniformis penicillinase, whereas the S. aureus enzyme had only about 40% of its residues in common with beta-lactamase I. These results are discussed with reference to the possible evolutionary relationships existing between known beta-lactamases. Detailed evidence for the amino acid sequence proposed has been deposited as Supplementary Publication SUP 50044 (27 pages) at the British Library (Lending Division), Boston Spa, Wetherby, W. Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1975), 145, 5.

| S-EPMC1165445 | biostudies-other

The composition of beta-lactamase I and beta-lactamase II from Bacillus cereus 569-H.

Project description:1. Crystalline beta-lactamase I from Bacillus cereus 569/H yielded only amino acids on acid hydrolysis, but crystalline beta-lactamase II from the same organism yielded also substantial quantities of neutral sugars and amino sugars. 2. Analysis with an amino acid analyser indicated that the two enzymes were similar though not identical in overall amino acid composition. Analysis of neutral and amino sugars as their silyl derivatives by gas-liquid chromatography showed that the carbohydrate moiety of beta-lactamase II contained residues of glucose, galactose, mannose, fucose, glucosamine and galactosamine. 3. After oxidation and hydrolysis both beta-lactamases gave small amounts of cysteic acid. After treatment of inactive Zn(2+)-free beta-lactamase II with N-ethylmaleimide or iodoacetate enzymic activity was not restored by the addition of Zn(2+).

| S-EPMC1179215 | biostudies-other

The Role of Active Site Flexible Loops in Catalysis and of Zinc in Conformational Stability of Bacillus cereus 569/H/9 β-Lactamase.

Project description:Metallo-β-lactamases catalyze the hydrolysis of most β-lactam antibiotics and hence represent a major clinical concern. The development of inhibitors for these enzymes is complicated by the diversity and flexibility of their substrate-binding sites, motivating research into their structure and function. In this study, we examined the conformational properties of the Bacillus cereus β-lactamase II in the presence of chemical denaturants using a variety of biochemical and biophysical techniques. The apoenzyme was found to unfold cooperatively, with a Gibbs free energy of stabilization (ΔG(0)) of 32 ± 2 kJ·mol(-1) For holoBcII, a first non-cooperative transition leads to multiple interconverting native-like states, in which both zinc atoms remain bound in an apparently unaltered active site, and the protein displays a well organized compact hydrophobic core with structural changes confined to the enzyme surface, but with no catalytic activity. Two-dimensional NMR data revealed that the loss of activity occurs concomitantly with perturbations in two loops that border the enzyme active site. A second cooperative transition, corresponding to global unfolding, is observed at higher denaturant concentrations, with ΔG(0) value of 65 ± 1.4 kJ·mol(-1) These combined data highlight the importance of the two zinc ions in maintaining structure as well as a relatively well defined conformation for both active site loops to maintain enzymatic activity.

| S-EPMC4965562 | biostudies-literature

Separation, purification and properties of beta-lactamase I and beta-lactamase II from Bacillus cereus 569/H/9.

Project description:1. A procedure was devised which is suitable for the isolation of beta-lactamase I and beta-lactamase II from Bacillus cereus 569/H/9 on a large scale. After adsorption on to Celite both enzymes were eluted in good yield and separated by chromatography on Sephadex CM-50. 2. beta-Lactamase I was separated into three main components by isoelectric focusing and into two components by chromatography. 3. The Zn(2+)-requiring beta-lactamase II obtained by this procedure had a lower molecular weight (22000) than beta-lactamase I (28000) and also differed from the latter in containing one cysteine residue. 4. The beta-lactamase II contained no carbohydrate, but showed the thermostability of the enzyme isolated earlier as a protein-carbohydrate complex. 5. Amino acid analyses and tryptic-digest ;maps' indicate that some degree of homology between beta-lactamase I and beta-lactamase II is possible, but that beta-lactamase I is not composed of the entire sequence of beta-lactamase II together with an additional peptide fragment. 6. A 6-methylpenicillin and a 7-methylcephalosporin showed much lower affinities for both enzymes than did penicillins and cephalosporins themselves.

| S-EPMC1168359 | biostudies-other

Purification and properties of two extracellular beta-lactamases from Bacillus cereus 569-H.

Project description:1. When Bacillus cereus 569/H was grown in a casamino acid (casein-hydrolysate) medium containing zinc sulphate rapid production of extracellular beta-lactamase II preceded that of beta-lactamase I. 2. beta-Lactamase I was separated from beta-lactamase II by fractional precipitation with ammonium sulphate. 3. beta-Lactamase I was purified by a process involving chromatography on Celite and DEAE-cellulose and beta-lactamase II by chromatography on DEAE-cellulose after denaturation of beta-lactamase I by heat. Both enzymes were obtained in crystalline form. 4. beta-Lactamase II prepared in this way appeared to have a higher molecular weight than beta-lactamase I and required Zn(2+) as a cofactor for both cephalosporinase and penicillinase activities.

| S-EPMC1179213 | biostudies-other

Mutational analysis of the two zinc-binding sites of the Bacillus cereus 569/H/9 metallo-beta-lactamase.

Project description:The metallo-beta-lactamase BcII from Bacillus cereus 569/H/9 possesses a binuclear zinc centre. The mono-zinc form of the enzyme displays an appreciably high activity, although full efficiency is observed for the di-zinc enzyme. In an attempt to assign the involvement of the different zinc ligands in the catalytic properties of BcII, individual substitutions of selected amino acids were generated. With the exception of His(116)-->Ser (H116S), C221A and C221S, the mono- and di-zinc forms of all the other mutants were poorly active. The activity of H116S decreases by a factor of 10 when compared with the wild type. The catalytic efficiency of C221A and C221S was zinc-dependent. The mono-zinc forms of these mutants exhibited a low activity, whereas the catalytic efficiency of their respective di-zinc forms was comparable with that of the wild type. Surprisingly, the zinc contents of the mutants and the wild-type BcII were similar. These data suggest that the affinity of the beta-lactamase for the metal was not affected by the substitution of the ligand. The pH-dependence of the H196S catalytic efficiency indicates that the zinc ions participate in the hydrolysis of the beta-lactam ring by acting as a Lewis acid. The zinc ions activate the catalytic water molecule, but also polarize the carbonyl bond of the beta-lactam ring and stabilize the development of a negative charge on the carbonyl oxygen of the tetrahedral reaction intermediate. Our studies also demonstrate that Asn(233) is not directly involved in the interaction with the substrates.

| S-EPMC1222521 | biostudies-other

Identification of beta-lactamase in antibiotic-resistant Bacillus cereus spores.

Project description:Beta-lactamase type I is reported for the first time to occur in the sporulated form in a penicillin-resistant Bacillus species. The enzyme was readily characterized from the B. cereus 5/B line (ATCC 13061) by mass spectrometry and two-dimensional gel electrophoresis.

| S-EPMC2227700 | biostudies-literature

Production of a variant of beta-lactamase II with selectively decreased cephalosporinase activity by a mutant of Bacillus cereus 569/H/9.

Project description:1. Mutants of Bacillus cereus 569/H/9 have been screened in a search for strains that synthesize variants of beta-lactamase II. 2. One of these mutants (strain 569/H/9/1) produces a beta-lactamase II-like enzyme that shows a selective decrease in cephalosporinase activity. 3. beta-Lactamase II from strain 569/H/9/1 has been purified to apparent homogeneity and its kinetic properties have been examined. This enzyme resembles the parent beta-lactamase II in its relative activity with benzylpenicillin as substrate when Zn(II) is replaced by other metal ions, but differs detectably from the parent enzyme in its isoelectric point.

| S-EPMC1162187 | biostudies-other

Engineered mononuclear variants in Bacillus cereus metallo-beta-lactamase BcII are inactive.

Project description:Metallo-beta-lactamases (MbetaLs) are zinc enzymes able to hydrolyze almost all beta-lactam antibiotics, rendering them inactive, at the same time endowing bacteria high levels of resistance. The design of inhibitors active against all classes of MbetaLs has been hampered by their structural diversity and by the heterogeneity in metal content in enzymes from different sources. BcII is the metallo-beta-lactamase from Bacillus cereus, which is found in both the mononuclear and dinuclear forms. Despite extensive studies, there is still controversy about the nature of the active BcII species. Here we have designed two mutant enzymes in which each one of the metal binding sites was selectively removed. Both mutants were almost inactive, despite preserving most of the structural features of each metal site. These results reveal that neither site isolated in the MbetaL scaffold is sufficient to render a fully active enzyme. This suggests that only the dinuclear species is active or that the mononuclear variants can be active only if aided by other residues that would be metal ligands in the dinuclear species.

| S-EPMC2565585 | biostudies-literature

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