SURFACE-ASSOCIATED SERINE-THREONINE KINASE IN SCHISTOSOMA-MANSONI

Existing evidence suggests that parasites of the genus Schistosoma are responsive to external stimuli derived from the host and from parasit es of the opposite sex. We hypothesize that these interactions are med iated by receptors at the parasite surface. To begin to address this i ssue, we have employed surface labelling by biotinylation to identify and isolate the surface molecules of adult S. mansoni. Isolated surfac e molecules were subsequently analyzed for the presence of protein kin ases, since protein kinase activity is frequently associated with sign al-transducing receptors. Our results demonstrate that serine-threonin e kinase activity is associated with the parasite surface and that sur face proteins of 145, 125, 95 and 57 kDa became phosphorylated on seri ne and threonine residues under in vitro conditions. No significant ty rosine phosphorylation of surface molecules was detected, despite the presence of many tyrosine-phosphorylated proteins in tegumental extrac ts. An additional unexpected finding of these studies was that adult s chistosomes express considerably more surface molecules than previousl y indicated by radioiodination studies, and that the majority of these molecules are of parasite rather than host origin.