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 C-14-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 approximate to 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.