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See detailSite-Directed Mutagenesis of the Streptomyces R61 Dd-Peptidase. Catalytic Function of the Conserved Residues around the Active Site and a Comparison with Class-a and Class-C Beta-Lactamases
Hadonou, Ayaovi Medard; Wilkin, Jean-Marc; Varetto, Louis ULg et al

in European Journal of Biochemistry (1992), 207(1), 97-102

The importance of various residues in the Streptomyces R61 penicillin-sensitive DD-peptidase has been assessed by site-directed mutagenesis. The replacement of the active Ser62 by a Cys residue yielded an ... [more ▼]

The importance of various residues in the Streptomyces R61 penicillin-sensitive DD-peptidase has been assessed by site-directed mutagenesis. The replacement of the active Ser62 by a Cys residue yielded an inactive protein which was also unable to recognize penicillin. The activity of the Lys65 → Arg mutant with the peptide and thiol ester substrates was decreased 100-200-fold and the rate of penicillin inactivation was decreased 20 000-fold or more. The mutant thus behaved as a poor, but penicillin-resistant, DD-peptidase. The other studied mutations, the mutations Phe358 → Leu, Tyr90 → Asn, Thr101 → Asn, Phe164 → Ala, Asp225 → Glu and Asp225 → Asn had little influence on the catalytic and penicillin-binding properties. The Asp225 mutants did not exhibit an increased sensitivity to cefotaxime. The Phe164 → Ala mutant was significantly more unstable than the wild-type enzyme. [less ▲]

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See detailThe Importance of the Negative Charge of Beta-Lactam Compounds in the Interactions with Active-Site Serine Dd-Peptidases and Beta-Lactamases
Varetto, Louis ULg; De Meester, Fabien; Monnaie, Didier et al

in Biochemical Journal (1991), 278(Pt 3), 801-807

The interaction between various penicillins and cephalosporins the carboxylate group of which at C-3 or C-4 had been esterified or amidated and different penicillin-recognizing enzymes was studied. In ... [more ▼]

The interaction between various penicillins and cephalosporins the carboxylate group of which at C-3 or C-4 had been esterified or amidated and different penicillin-recognizing enzymes was studied. In general, our findings reinforced the common assumption that an anionic group at that position is necessary for the effective acylation of these enzymes. However, the relative activities of the modified beta-lactams as inactivators of the Streptomyces R61 DD-peptidase or as substrates of the Bacillus licheniformis, Streptomyces albus G and Enterobacter cloacae beta-lactamases did not fit a general scheme in which the intrinsic electronic and geometric properties of the beta-lactam compounds would be sufficient to explain their substrate or inactivator properties towards the various types of enzymes investigated. [less ▲]

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See detailStructure-Activity Relationships in the Beta-Lactam Family: An Impossible Dream
Frère, Jean-Marie ULg; Joris, Bernard ULg; Varetto, Louis ULg et al

in Biochemical Pharmacology (1988), 37(1), 125-32

The difficulty of establishing structure-activity relationships in the beta-lactam family of antibiotics stems from the fact that: (1) The targets in various bacteria exhibit widely different ... [more ▼]

The difficulty of establishing structure-activity relationships in the beta-lactam family of antibiotics stems from the fact that: (1) The targets in various bacteria exhibit widely different sensitivities. (2) Some bacteria produce beta-lactamases, enzymes capable of destroying the antibiotics. The rates of the reactions with the beta-lactamases and the target enzymes are not necessarily related. (3) In Gram-negative bacteria, the diffusion rate through the outer membrane varies independently from the two other factors. [less ▲]

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See detailThe importance of the negative charge of β-lactam compounds for the inactivation of the active-site serine DD-peptidase of Streptomyces R61
Varetto, Louis ULg; Frère, Jean-Marie ULg; Ghuysen, Jean-Marie ULg

in FEBS Letters (1987), 225(1-2), 218-222

The interaction between the Streptomyces R61 penicillin-sensitive DD-peptidase and deacetyl-cephalosporin C or its lactone derivative has been studied at different pH values. The results show the ... [more ▼]

The interaction between the Streptomyces R61 penicillin-sensitive DD-peptidase and deacetyl-cephalosporin C or its lactone derivative has been studied at different pH values. The results show the importance of an enzyme group of pK approximately equal to 9 which might form an ion pair with the free carboxylate of the former compound. This electrostatic interaction is shown to contribute to the formation of the first, non-covalent enzyme-inactivator complex by a factor of at least 50. [less ▲]

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