SEQUENCE OF AN AVIAN NONMUSCLE CALDESMON

We have sequenced a cloned cDNA from a chicken gizzard library which encodes a short version of caldesmon with the properties expected for the non-muscle protein. The predicted protein is 524 amino acids long with a molecular mass of 60 174 daltons. Expression in bacteria produces a protein with an apparent molecular weight on SDS gels of 75-77 000, that comigrates with human platelet caldesmon. The expressed protein binds to F-actin and is retained on calmodulin-Sepharose in the presence, but not absence of Ca2+. This non-muscle caldesmon isoform is identical to the smooth muscle protein at the N- and C-terminal ends, but is missing 232 amino acids from the centre. This central segment is thought to be helical, suggesting that non-muscle caldesmon is approximately 35 nm shorter, about 40 nm overall length, than smooth muscle caldesmon.