Comparative sequence analysis of the complete human sarcomeric myosin heavy chain family: implications for functional diversity.

The conventional myosin motor proteins that drive mammalian skeletal and cardiac muscle contraction include eight sarcomeric myosin heavy chain (MyHC) isoforms. Six skeletal MyHCs are encoded by genes found in tightly linked clusters on human and mouse chromosomes 17 and 11, respectively. The full coding regions of only two out of six mammalian skeletal MyHCs had been sequenced prior to this work. In an effort to assess the extent of sequence diversity within the human MyHC family we present new full-length coding sequences corresponding to four additional human genes: MyHC-IIb, MyHC-extraocular, MyHC-IIa and MyHC-IIx/d. This represents the first opportunity to compare the full coding sequences of all eight sarcomeric MyHC isoforms within a vertebrate organism. Sequence variability has been analyzed in the context of available structure/function data with an emphasis on potential functional diversity within the family. Results indicate that functional diversity among MyHCs is likely to be accomplished by having small pockets of sequence diversity in an otherwise highly conserved molecule.