AMINO-ACID-SEQUENCE OF THE LIGHT-CHAIN OF ACANTHAMOEBA MYOSIN IC

The amino acid sequence of the light chain of Acanthamoeba myosin IC d educed from the cDNA sequence comprises 149 amino acids with a calcula ted molecular weight of 16739. All but the 3 N-terminal residues were also determined by amino acid sequencing of the purified protein, whic h also showed the N-terminus to be blocked. Phylogenetic analysis show s Acanthamoeba myosin IC light chain to be more similar to the calmodu lin subfamily of EF-hand calcium-modulated proteins than to the myosin II: essential light chain or regulatory Light chain subfamilies. In p airwise comparisons, the myosin IC light chain sequence is most simila r to sequences of calmodulins (similar to 50% identical) and a squid c alcium-binding protein (similar to 43% identical); the sequence is sim ilar to 37% identical to the calcium-binding essential light chain of Physarum myosin II and similar to 30% identical to the essential light chain of Acanthamoeba myosin II, and the essential light chain and re gulatory light chain of Dictyostelium myosin II. The sequence predicts four helix-loop-helix domains with possible calcium-binding sites in domains I and III, suggesting that calcium may affect the activity of this unconventional myosin. This is the first report of the sequence o f an unconventional myosin light chain other than calmodulin.