Reference : Use of model enzymes in the determination of the mode of action of penicillins and ∆3...
Scientific journals : Article
Life sciences : Microbiology
Life sciences : Biochemistry, biophysics & molecular biology
http://hdl.handle.net/2268/83042
Use of model enzymes in the determination of the mode of action of penicillins and ∆3-cephalosporins
English
Ghuysen, Jean-Marie [Université de Liège - ULiège > Faculté de Médecine, Institut de Botanique > Service de Microbiologie > > >]
Frère, Jean-Marie mailto [Université de Liège - ULiège > Faculté de Médecine, Institut de Botanique > Service de Microbiologie > >]
Leyh-Bouille, Mélina [Université de Liège - ULiège > Faculté de Médecine, Institut de Botanique > Service de Microbiologie > > >]
Coyette, Jacques [Université de Liège - ULiège > Faculté de Médecine, Institut de Botanique > Service de Microbiologie > > >]
Dusart, Jean [Université de Liège - ULiège > Faculté de Médecine, Institut de Botanique > Service de Microbiologie > >]
Nguyen-Distèche, Martine mailto [Université de Liège - ULiège > Faculté de Médecine, Institut de Botanique > Service de Microbiologie > >]
1-Jan-1979
Annual Review of Biochemistry
Annual Reviews
48
73-101
Yes (verified by ORBi)
International
0066-4154
1545-4509
Palo Alto
CA
[en] acyltransferases/*metabolism ; binding Sites ; carboxypeptidases/*metabolism ; cephalosporins/pharmacology ; enterococcus faecalis/enzymology ; enzyme activation ; molecular weight ; penicillins/pharmacology ; peptidyl transferases/*metabolism ; protein binding ; streptomyces/enzymology ; structure-activity relationship
[en] Studies carried out with exocellular penicillin-sensitive enzymes (PSEs) from various strains of actinomycetes (the only organisms known to excrete such enzymes during growth), show that:
(a) The penam or 3-cephem nuclei are the main portion of the antibiotic molecules concerned with the initial reversible binding to the enzyme. Binding to the enzyme active center is neither very selective nor very efficient but it has specific effects on the enzyme conformation. The sites thus induced in the enzyme react with suitably oriented and structured N14 substituents and force the β-lactam ring to gain a much increased chemical reactivity. As the β-lactam ring opens (with the help of electron attracting groups) and achieves acylation of the enzyme, the thiazolidine or dihydrothiazine ring interacts with a nearby site thus greatly increasing the stability of the acyl-enzyme complex.
(b) Elimination of the bound residue and regeneration of a free active enzyme by deacylation in the presence of a suitable exogenous nucleophile may proceed according to two different pathways. PSEs slowly overcome the stabilizing effect of the bound penicilloyl molecule by C5-C6 cleavage; deacylation of the N-acylglycyl-enzyme complex thus formed is then immediate whereas the other fragmentation product is further processed and eventually released as N-formyl-D-penicillamine. Alternatively, fragmentation does not occur and the bound residue is slowly eliminated as a whole. Irrespective of the pathway, the overall reactions between PSEs and β-lactams are characterized by very low turnover numbers.
(c) In some respects the above mechanism resembles that through which analogues of the natural substrates, L-R-D-Ala-D-Ala-terminated peptides (where R is an amino acid residue), interact with the PSEs. The D-Ala-D-Ala portion is mainly responsible for the initial binding whereas a suitable side chain in the preceding L residue is required to induce enzyme action on the bound peptide, which forces the D-Ala-D-Ala amide linkage to lose all double bond character. However, whether the enzyme functions as a catalyst template or forms a transitory acyl intermediate, the transfer of the L-R-D -Ala moiety to the exogenous nucleophile is rapid, and therefore the reactions are characterized by high turnover numbers.
(d) Depending upon the PSEs, the independence between the penicillin and L-R-D-Ala-D-Ala active centers is more or less pronounced. Indirect but strong evidence suggests that the physiological function of the β-lactam center in the PSEs may be regulatory rather than catalytic. By interacting with it, the β-lactam inactivates the specific catalytic center of the enzyme thus preventing action on natural substrate analogues.
Exocellular PSEs are probably not physiologically important whereas the membrane-bound components (or at least some of them) are likely to be crucial in mediating the antibacterial β-lactam effect. The relevance of the exocellular model systems to the actual problem of the mechanism of penicillin action has been examined by extending the above studies to several membrane-bound PSEs originating from taxonomically unrelated bacteria. The data suggest that they react with β-lactam antibiotics according to the same basic mechanism as that described above.
National Institutes of Health - NIH
Researchers ; Professionals
http://hdl.handle.net/2268/83042
10.1146/annurev.bi.48.070179.000445

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