Cloning of a phospholipase C-delta 1 of rabbit skeletal muscle.

The phospholipase C isoform responsible for the increase in the total myoplasmic inositol 1,4,5-trisphosphate concentration during tetanic contraction of isolated skeletal muscle and its mechanism of activation is not known. We have cloned and sequenced a phospholipase C cDNA of rabbit skeletal muscle coding for a protein of 745 amino acids with a molecular mass of 84,440 kDa. The deduced amino acid sequence exhibits the phospholipase C-specific domains X and Y which according to current knowledge very likely represent the catalytic centre of the enzyme. An overall sequence homology of 88% to the phospholipase C-delta 1 of rat brain suggests that the encoded protein represents a phospholipase C-delta 1 isoform of rabbit skeletal muscle. Northern blot analysis shows, that this phospholipase C-delta is dominantly expressed in skeletal muscle, less strongly in smooth muscle (uterus) and lung and weakly in heart, kidney and brain. In the N-terminal part of the primary structure a consensus sequence for a canonical EF-hand Ca2+ binding domain can be identified together with a short positively charged motif which recently has been suggested to be essential for the binding of phosphatidylinositol 4,5-bisphosphate. If these two domains which are unique for phospholipase C-delta are sufficient in establishing a mechanism for the activation of the enzyme, inositol 1,4,5-trisphosphate formation in skeletal muscle could be the consequence of an increase in myoplasmic Ca2+.