Bacillus licheniformis β-lactamases: multiple forms and their roles

B. licheniformis 749/C secretes a hydrophilic penicillinase (detected by immunoprecipitation) which is a precursor of the usually isolated 29 500 molecular mass exoenzyme. This larger form carries an eight amino acid N-terminal extension with the sequence: Ser-Gln-Pro-Ala-Glu-Lys-Asn-Glu-exoenzyme (K Izui, J. B. K. Nielsen, M. Caulfield & J. O. Lampen, unpublished results; K. Simons, personal communication). Translation of 749/C mRNA in an in-vitro protein synthesizing system from Escherichia coli yields an active hydrophobic penicillinase of molecular mass 34 000-36 000 with an N-terminal extension (C. N. Chang, K. Izui, G. Blobel & J. O. Lampen, unpublished results; M. Sarvas et al. (1978) FEBS Lett. 95, 76). Partial sequence data how at least one Lys residue in the 16 residues adjacent to the N-terminal Lys of exoenzyme. Both sequences are incompatible with the relatively polar, Lys-free extension reported for the previously characterized 33 000 molecular mass membrane-bound form (S. Yamamoto & J. O. Lampen (1976), Proc. natn, Acad. Sci. U.S.A. 73, 1457-1461). The biosynthetic interrelations among the several forms are discussed.