Membrane penicillinase of Bacillus licheniformis 749/C:sequence and possible repeated tetrapeptide structure of the phospholipopeptide region.

Abstract

The membrane penicillinase (EC 3.5.2.6; penicillin amido-.beta.-lactamhydrolase) of B. licheniformis 749/C, which may be an intermediate in the formation of the exoenzyme, is a phospholipoprotein that carries an NH2-terminal chain of 24 amino acids (only serine, glycine, aspartic acid, asparagine, glutamic acid and glutamine) and a phosphatidylserine that is not present in the exoenzyme. Trypsin cleavage of the membrane enzyme produces a 26-residue phospholipopeptide whose sequence is: phosphatidylserine-Asn-Asp-Glu-Gly-Asp-Ser-Gly-Asn-Gln-Ser-Gly-Asp-Gly-Asn-Gln-Ser-Glu-Glu-Asn-Glu-Asp-Gln-Ser-Lys-COOH. This segment was derived from a tetrapeptide [Asp(or Asn)-Glu(or Gln)-Ser-Gly] by a series of mutations (which required reasonable base transitions and transversions), 4 deletions and 1 insertion. The putative mRNA for the peptide chain would have a high purine content (up to 80%) and a structure resembling poly A. The phospholipopeptide is long enough to span the lipid bilayer of the membrane. Hence, the phosphatidylserine residue may be on either face of the membrane and still allow the major catalytic portion of the enzyme to be in the external aqueous phase.