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Active-site serine mutants of the Streptomyces albus G beta-lactamase.

ABSTRACT: By using site-directed mutagenesis, the active-site serine residue of the Streptomyces albus G beta-lactamase was substituted by alanine and cysteine. Both mutant enzymes were produced in Streptomyces lividans and purified to homogeneity. The cysteine beta-lactamase exhibited a substrate-specificity profile distinct from that of the wild-type enzyme, and its kcat./Km values at pH 7 were never higher than 0.1% of that of the serine enzyme. Unlike the wild-type enzyme, the activity of the mutant increased at acidic pH values. Surprisingly, the alanine mutant exhibited a weak but specific activity for benzylpenicillin and ampicillin. In addition, a very small production of wild-type enzyme, probably due to mistranslation, was detected, but that activity could be selectively eliminated. Both mutant enzymes were nearly as thermostable as the wild-type.

SUBMITTER: Jacob F

PROVIDER: S-EPMC1151291 | biostudies-other | 1991 Aug

REPOSITORIES: biostudies-other

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Mechanism of acyl transfer by the class A serine beta-lactamase of Streptomyces albus G.

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