Bacillus licheniformis penicillinase: cleavages and attachment of lipid during cotranslational secretion.

Abstract

The penicillinase (EC 3.5.2.6) of B. licheniformis is secreted cotranslationally. In extracts is was formed by membrane-associated but not by free polysomes; and after extracellular labeling of cells, followed by completion of the growing chains on polysomes in vitro, labeled penicillinase could be immunoprecipitated. This product contained electrophoretic peaks of MW 36,000, 33,000 and 29,000, which correspond to previously reported forms of the enzyme. The 36,000 MW form exhibits moderate hydrophobicity, as expected of a precursor with an NH2-terminal signal sequence for secretion. In addition, part of the 33,000 MW fraction evidently contains lipid: it is even more hydrophobic, and [2-3H]glycerol was incorporated into these molecules but not into the other forms of the enzyme. These findings renew the earlier, discarded suggestion that the 33,000 MW membrane-bound penicillinase in the cells contains lipid. The incorporation of lipid and 2 different cleavages can evidently all occur during growth of the penicillinase chain. The resulting terminal regions are all accessible to extracellular labeling on growth chains. Several additional, unidentified lipoproteins also incorporate lipid during chain growth.