Dissociation of Mycoplasma gallisepticum membranes with lithium diiodosalicylate and isolation of glycoprotein.
M. gallisepticum membranes were treated with 0.3M lithium diiodosalicylate (LIS) and, on average, 43% of the original membrane proteins were extracted. The extract contained particles with a sedimentation coefficient of 13S and some aggregated proteins. This LIS extract was immunogenic, stimulating the production of haemagglutination-inhibiting, growth-inhibiting and precipitating antibodies in rabbits. It was devoid of haemagglutinating (HA) activity for chicken erythrocytes but did inhibit the HA activity of membranes of M. gallisepticum. This inhibitory activity was destroyed by periodate and trypsin, but not by heat. By sedimentation equilibrium in a caesium chloride gradient, the LIS extract was separated into a lipoprotein-like and a glycoprotein fraction. The lipoprotein-like fraction contained the majority of the proteins present in the original extract, had HA activity and blocked antibody which inhibits haemagglutination. These activities were apparently due to the protein moiety, since they were not removed by extraction with n-butanol. The lipoprotein-like fraction behaved similarly to the unfractionated LIS extract in immunodiffusion tests and polyacrylamide gel electrophoresis, producing one periodic acid-Schiff positive band in the latter. The glycoprotein fraction consisted of about 66% carbohydrate and 33% protein. The sugar components were identified as glucose, galactose, glucosamine, galactosamine, glucuronic acid. The glycorprotein fraction did not possess HA but blocked the HA activity of M. gallisepticum membranes. In immunodiffusion it produced one faint precipitation band. The possible significance of glycoprotein in mycoplasma membranes has been discussed.