Acylation and immunological properties of Mycoplasma gallisepticum membrane proteins.

The acylation of Mycoplasma gallisepticum membrane proteins was studied by electrophoresis after in vivo labelling with different 14C-fatty acids and by chemical analysis. The immunological properties of these proteins were investigated by Western blotting and crossed immunoelectrophoresis. Among the ca. 200 membrane polypeptides resolved by two-dimensional electrophoresis, 35 components (including the major protein p67) were covalently modified with acyl chains. These acylated proteins displayed lower pls than average (5.0-7.4 vs. 5.0-9.0) and proved to be the major membrane protein antigens and immunogens of M. gallisepticum. The apparent selectivity of fatty acid incorporation into proteins was, as suggested by in vivo labelling: palmitic acid (16:0) > myristic acid (14:0) > oleic acid (18:1c) > stearic acid (18:0) > linoleic acid (18:2c). However, the true order of selectivity, as revealed by chemical analysis, proved to be 18:2c > 16:0 > 18:1c > 18:0 > 14:0. More specifically, palmitic acid was the major O-ester-bound fatty acid and linoleic acid the major amide-linked fatty acid. The observed average ratio [O-ester-bound + amide-linked acyl chains]/O-ester-bound chains approximately 1.4 and the presence of S-glycerylcysteine suggest that, in M. gallisepticum, membrane proteins are lipid-modified according to a mechanism identical to that depicted for lipoproteins of Gram-negative eubacteria.