Myosin Transducer Inter-Strand Communication Is Critical for Normal ATPase Activity and Myofibril Structure

Abstract

The R249Q mutation in human β-cardiac myosin results in hypertrophic cardiomyopathy. We previously showed that inserting this mutation into Drosophila melanogaster indirect flight muscle myosin yields mechanical and locomotory defects. Here, we use transgenic Drosophila mutants to demonstrate that residue R249 serves as a critical communication link within myosin that controls both ATPase activity and myofibril integrity. R249 is located on a β-strand of the central transducer of myosin, and our molecular modeling shows that it interacts via a salt bridge with D262 on the adjacent β-strand. We find that disrupting this interaction via R249Q, R249D or D262R mutations reduces basal and actin-activated ATPase activity, actin in vitro motility and flight muscle function. Further, the R249D mutation dramatically affects myofibril assembly, yielding abnormalities in sarcomere lengths, increased Z-line thickness and split myofibrils. These defects are exacerbated during aging. Re-establishing the β-strand interaction via a R249D/D262R double mutation restores both basal ATPase activity and myofibril assembly, indicating that these properties are dependent upon transducer inter-strand communication. Thus, the transducer plays an important role in myosin function and myofibril architecture.

Filamin protects myofibrils from contractile damage through changes in its mechanosensory region

“…Similar enlarged Z-disc phenotypes like the one in filamin open mutants have been shown before from a diverse set of genetic conditions and sometimes are referred to as zebra bodies. For example, by affecting the tension generated by myofibril contraction through a mutation in the motor domain in the myosin heavy chain ( MHC R249D ; [ 45 ]), by reducing the amount of myosin-II, or its regulatory light chain [ 46 ], or by overexpressing truncated forms of the M-line protein Sals [ 47 ]. In addition, massively affecting transcription or translation of IFM-specific genes also leads to enlarged Z-discs [ 48 , 49 ].…”

Untitled

“…Similar enlarged Z-disc phenotypes like the one in filamin open mutants have been shown before from a diverse set of genetic conditions and sometimes are referred to as zebra bodies. For example, by affecting the tension generated by myofibril contraction through a mutation in the motor domain in the myosin heavy chain (MHC R249D ; [45]), by reducing the amount of myosin-II, or its regulatory light chain [46], or by overexpressing truncated forms of the Mline protein Sals [47]. In addition, massively affecting transcription or translation of IFM-specific genes also leads to enlarged Z-discs [48,49].…”

Untitled

“…Similar enlarged Z-disc phenotypes like the one in filamin open mutants have been shown before from a diverse set of genetic conditions and sometimes are referred to as zebra bodies. For example, by affecting the tension generated by myofibril contraction through a mutation in the motor domain in the myosin heavy chain (MHC R249D ; [45]), by reducing the amount of myosin-II, or its regulatory light chain [46], or by overexpressing truncated forms of the Mline protein Sals [47]. In addition, massively affecting transcription or translation of IFM-specific genes also leads to enlarged Z-discs [48,49].…”