Identification of serine/threonine protein kinases secreted by Trichinella spiralis infective larvae.

Serine/threonine protein kinase activity was identified in excretory/secretory (ES) products of Trichinella spiralis infective larvae, via phosphorylation of exogenous and endogenous substrates. Protein kinase activity was identified as an authentic secretory product via blockade of release into culture medium by brefeldin A. Enzyme activity was reductant-dependent, and the relative resistance to a panel of inhibitors suggested that it could not be readily assigned to any of the major documented subfamilies of serine/threonine protein kinases. There was no evidence for protein tyrosine kinase activity in ES products. The major phosphorylated proteins in this compartment resolved at 50 and 55 kDa by SDS-PAGE, and are therefore designated pp50/55. These proteins contained mainly phosphoserine, and appear to represent differentially glycosylated variants of a 35 kDa polypeptide, modified via the addition of three and four N-linked oligosaccharides, respectively. An autophosphorylation assay following separation by SDS-PAGE identified two protein kinases of 70 and 135 kDa in ES products.