MYOPHILIN OF ECHINOCOCCUS-GRANULOSUS - ISOFORMS AND PHOSPHORYLATION BY PROTEIN-KINASE-C

Myophilin is a muscle-associated antigen of the taeniid cestode Echino coccus granulosus. This protein shows a high amino acid sequence homol ogy with calponins and calponin-like proteins, which are proposed to b e associated with the regulation of smooth muscle contraction. In orde r to provide supportive evidence for a relationship between these prot eins, we characterized myophilin using electrophoretic, biochemical an d molecular biological approaches. Two-dimensional protein electrophor etic separation of E. granulosus larval proteins defined 4 isoelectric isoforms of myophilin (alpha, beta, gamma and delta), which appeared to be a consequence of post-translational modification of a single gen e product. It was also demonstrated biochemically that E. granulosus m yophilin undergoes specific phosphorylation in vitro by protein kinase C (PKC). Finally, myophilin homologues were identified in extracts of Taenia hydatigena and T. ovis by immunoblot. A partial cDNA of the cl osely related species, E. multilocularis, was isolated by cloning proc edures and showed 99 % homology with the E. granulosus myophilin gene. The similarities of E. granulosus myophilin with calponins in their t issue localization, protein isoform patterns, ability to be phosphoryl ated in vitro by PKC, and the relatively conserved nature of the prote in among related parasites suggest that myophilin may be associated wi th smooth muscle contraction.