The kinetic properties of the carboxy terminal domain of the Bacillus licheniformis 749/I BlaR penicillin-receptor shed a new light on the derepression of beta-lactamase synthesis.
To study the properties of the BlaR penicillin-receptor involved in the induction of the Bacillus licheniformisbeta-lactamase, the water-soluble carboxy terminal domain of the protein (BlaR-CTD) was overproduced in the periplasm of Escherichia coli JM105 and purified to protein homogeneity. Its interactions with various beta-lactam antibiotics were studied. The second-order acylation rate constants k2/K' ranged from 0.0017 to more than 1 micro M-1s-1 and the deacylation rate constants were lower than 4 x 10-5 s-1. These values imply a rapid to very rapid formation of a stable acylated adduct. BlaR-CTD is thus one of the most sensitive penicillin-binding proteins presently described. In the light of these results, the kinetics of beta-lactamase induction in Bacillus licheniformis were re-examined. When starting with a rather high cell density, a good beta-lactamase substrate such as benzylpenicillin is too sensitive to beta-lactamase-mediated hydrolysis to allow full induction. By contrast, a poor beta-lactamase substrate (7-aminocephalosporanic acid) can fully derepress beta-lactamase expression under conditions where interference of the antibiotic with cell growth is observed. These results suggest that acylation of the penicillin receptor is a necessary, but not sufficient, condition for full induction.
Duval
Valérie
V
Centre d'Ingénierie des Protéines, Université de Liège, Institut de Chimie B6a, Sart Tilman, Belgium.
Swinnen
Marc
M
Lepage
Sophie
S
Brans
Alain
A
Granier
Benoît
B
Franssen
Christine
C
Frère
Jean-Marie
JM
Joris
Bernard
B
D000215:Acylation; D001407:Bacillus / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D001426:Bacterial Proteins; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D002511:Cephalosporins / Q000494:pharmacology*; D015964:Gene Expression Regulation, Bacterial; D007700:Kinetics; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000378:metabolism; D001618:beta-Lactamases / Q000096:biosynthesis*; D047090:beta-Lactams / Q000378:metabolism / Q000494:pharmacology
D001426:Bacterial Proteins; D002352:Carrier Proteins; D002511:Cephalosporins; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D047090:beta-Lactams; C030735:7-aminocephalosporanic acid; D001618:beta-Lactamases