Val-237 for Ala substitution in the TEM-2 beta-lactamase dramatically alters the catalytic efficiencies towards carbenicillin and ticarcillin.
The mutant 554 of TEM-2 beta-lactamase was selected for a decrease in the resistance to carbenicillin of an Escherichia coli K12 carrier. The amino acid sequence of the mutant beta-lactamase was determined by manual Edman degradation analysis of proteolytic peptides. A single substitution Val for Ala was localized at position 237. The mutant exhibited only 2% of the catalytic efficiency of the wild-type enzyme towards carbenicillin and ticarcillin, whereas it retained 30-60% of the hydrolytic activity towards other penicillin and cephalosporin substrates. Carfecillin, the phenyl ester of the side-chain carboxyl group of carbenicillin, was hydrolysed as a good substrate. This suggests that the behaviour of the mutant enzyme towards carbenicillin may result from ionic rather than steric constraints. A molecular model of the Val-237 TEM-2 mutant suggests possible electrostatic interaction between Glu-171 and the carboxylic group of the side chain of carbenicillin.
Barthélémy
M
M
Muséum National Histoire Naturelle, CNRS URA 401, Paris, France.
Péduzzi
J
J
Rowlands
D
D
Paul
G
G
Moreau
G
G
Labia
R
R
D000595:Amino Acid Sequence; D002228:Carbenicillin / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D013329:Structure-Activity Relationship; D013982:Ticarcillin / Q000378:metabolism*; D001618:beta-Lactamases / Q000737:chemistry / Q000502:physiology*
D001618:beta-Lactamases; D013982:Ticarcillin; D002228:Carbenicillin