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Characterization of the membrane sensor PenJ for beta-lactam antibiotics from Bacillus licheniformis by amino acid substitution.

The PenJ protein of the penicillinase gene (penP) expression system from Bacillus licheniformis is an antirepressor and membrane receptor for beta-lactam antibiotics. A putative beta-lactam antibiotic binding site including Ser402 and Lys405, which are homologous to the conserved sequence for the beta-lactam binding site (Ser-X-X-Lys) is present. An amino acid substitution was introduced at Ser402 to Ala, removing the hydroxyl group of the serine. The mutant PenJ, S402A, was still functional. However, two other mutants, S402T (Ser402-->Thr) and K405A (Lys405-->Ala), were not functional. Thus, the hydroxyl group of Ser402 does not appear to be important for penicillin binding. Amino acid substitutions (K539R, D591N and K539R.G541V) were introduced in PenJ in the region of the putative phosphoryl binding domain. None of these mutant PenJ proteins was a functional antirepressor. These results suggested that the putative phosphoryl binding domain might be an important region for signal transduction.