Abstract
The myosin molecular motor interacts with actin filaments in an ATP-dependent manner to yield muscle contraction. Myosin heavy chain residue R369 is located within loop 4 at the actin-tropomyosin interface of myosin’s upper 50 kDa subdomain. To probe the importance of R369, we introduced a histidine mutation of that residue into Drosophila myosin and implemented an integrative approach to determine effects at the biochemical, cellular, and whole organism levels. Substituting the similarly charged but bulkier histidine residue reduces maximal actin binding in vitro without affecting myosin ATPase activity. R369H mutants exhibit impaired flight ability that is dominant in heterozygotes and progressive with age in homozygotes. Indirect flight muscle ultrastructure is normal in mutant homozygotes, suggesting that assembly defects or structural deterioration of myofibrils are not causative of reduced flight. Jump ability is also reduced in homozygotes. In contrast to these skeletal muscle defects, R369H mutants show normal heart ultrastructure and function, suggesting that this residue is differentially sensitive to perturbation in different myosin isoforms or muscle types. Overall, our findings indicate that R369 is an actin binding residue that is critical for myosin function in skeletal muscles, and suggest that more severe perturbations at this residue may cause human myopathies through a similar mechanism.
Highlights
Myosin II molecules incorporate into thick filaments in the sarcomeres of striated muscles and interact with disinhibited actin-containing thin filaments to produce force in an ATP-dependent fashion
Our results demonstrate that the R369H mutation decreases myosin maximal binding to F-actin in vitro and reduces locomotion in adult Drosophila, indicating that R369 is critical to both actin interaction and muscle function
We crossed the transgenes into the indirect flight muscle (IFM) and jump muscle myosin-null Mhc10 line [9] and selected fly lines with wild-type myosin to actin ratios, as determined by polyacrylamide gel electrophoresis analysis of the upper thoraces of young mutant flies
Summary
Myosin II molecules incorporate into thick filaments in the sarcomeres of striated muscles and interact with disinhibited actin-containing thin filaments to produce force in an ATP-dependent fashion. Mutations that affect this interaction can cause striated muscle disease. Myosin residue R369 (β-cardiac myosin amino acid numbering) resides on the tip of loop-4 of the upper 50 kDa subdomain and faces the outside of the molecule at an interface with actin and tropomyosin. The β-myosin heavy chain arginine to glutamine mutation (R369Q) caused dilated cardiomyopathy in a pediatric patient [4], suggesting a critical conserved role of the residue in striated muscles
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
