CHARACTERIZATION OF MUTANT MYOSINS OF DICTYOSTELIUM-DISCOIDEUM EQUIVALENT TO HUMAN FAMILIAL HYPERTROPHIC CARDIOMYOPATHY MUTANTS - MOLECULAR-FORCE LEVEL OF MUTANT MYOSINS MAY HAVE A PROGNOSTIC IMPLICATION

Recent studies have revealed that familial hypertrophic cardiomyopathy (FHC) is caused by missence mutations in myosin heavy chain or other sarcomeric proteins, To investigate the functional impact of FHC mutat ions in myosin heavy chain, mutants of Dictyostelium discoideum myosin II equivalent to human FHC mutations were generated by site-directed mutagenesis, and their motor function was characterized at the molecul ar level, These mutants, i.e., R397Q, F506C, G575R, A699R, K703Q, and K703W are respectively equivalent to R403Q, F513C, G584R, G716R, R719Q , and R719W FHC mutants, We measured the force generated by these myos in mutants as well as the sliding velocity and the actin-activated ATP ase activity, These measurements showed that the A699R, K703Q, and K70 3W myosins exhibited unexpectedly weak affinity with actin and the low est level of force, though their ATPase activity remained rather high, F506C mutant which has been reported to have benign prognosis exhibit ed the least impairment of the motile and enzymatic activities, The mo tor functions of R397Q and G575R myosins were classified as intermedia te, These results suggest that the force level of mutant myosin molecu le may be one of the key factors for pathogenesis which affect the pro gnosis of human FHC.