[36] N-terminal glyceride-cysteine modification of membrane penicillinases in gram-positive bacteria

This chapter deals with N-terminal glyceride-cysteine modification of membrane penicillinases in gram-positive bacteria. With improved procedures for purification and SDS-polyacrylamide gel electrophoresis, the membrane enzyme is shown to contain a hydrophilic N-terminal extension of 16 residues. The terminal cysteine carries a diglyceride in thioether linkage and a long-chain fatty acid in amide linkage. The identified lipoproteins from gram-positive bacteria are the membrane penicillinases of B. licheniformis strains 749 and 6346, the γ-penicillinase of B. cereus 569/H (now termed β-1actamase III), and the type A and C β-lactamases of Staphylococcus aureus. B. licheniformis 749 produces substantial quantities of a 63-kilodalton membrane protein which on brief treatment with trypsin yields a hydrophilic 60-kilodalton product that is present as well in the culture fluid. The lipoprotein modification includes two ester-linked (O-acyl) and one amide-linked (N-acyl) palmitate residues. The ester bond is cleaved in 0.1 N NaOH at 37° while the amide bond is stable. The amino acid residues preceding and following the cysteine residue that undergoes modification are conserved to a considerable extent.