The amino acid sequence of the light chain of Acanthamoeba myosin IC

The amino acid sequence of the light chain of Acanthamoebamyosin IC deduced from the cDNA sequence comprises 149 aminoacids with a calculated molecular weight of 16739. All but the 3N-terminal residues were also determined by amino acid sequencingof the purified protein, which also showed the N-terminus to beblocked. Phylogenetic analysis shows Acanthamoeba myosin IC lightchain to be more similar to the calmodulin subfamily of EF-handcalcium-modulated proteins than to the myosin II essential lightchain or regulatory light chain subfamilies. In pairwisecomparisons, the myosin IC light chain sequence is most similarto sequences of calmodulins (50% identical) and a squidcalcium-binding protein (43% identical); the sequence is37% identical to the calcium-binding essential light chainof Physarum myosin II and 30% identical to the essentiallight chain of Acanthamoeba myosin II, and the essential lightchain and regulatory light chain of Dictyostelium myosin II. Thesequence predicts four helix-loop-helix domains with possiblecalcium-binding sites in domains I and III, suggesting thatcalcium may affect the activity of this unconventional myosin.This is the first report of the sequence of an unconventionalmyosin light chain other than calmodulin