An alternative domain near the ATP binding pocket of Drosophila myosin affects muscle fiber kinetics.
We examined the importance of alternative versions of a region near the ATP binding site of Drosophila myosin heavy chain for muscle mechanical properties. Previously, we exchanged two versions of this region (encoded by alternative exon 7s) between the indirect flight muscle myosin isoform (IFI) and an embryonic myosin isoform (EMB) and found, surprisingly, that in vitro solution actin-activated ATPase rates were increased (higher Vmax) by both exon exchanges. Here we examined the effect of increased ATPase rate on indirect flight muscle (IFM) fiber mechanics and Drosophila locomotion. IFM expressing EMB with the exon 7a domain replaced by the IFM specific exon 7d domain (EMB-7d) exhibited 3.2-fold greater maximum oscillatory power (Pmax) and 1.5-fold greater optimal frequency of power generation (fmax) versus fibers expressing EMB. In contrast, IFM expressing IFI with the exon 7d region replaced by the EMB exon 7a region (IFI-7a), showed no change in Pmax, fmax, step response, or isometric muscle properties compared to native IFI fibers. A slight decrement in IFI-7a flight ability was observed, suggesting a negative influence of the increased ATPase rate on Drosophila locomotion, perhaps due to energy supply constraints. Our results show that exon 7 plays a substantial role in establishing fiber speed and flight performance, and that the limiting step that sets ATPase rate in Drosophila myosin has little to no direct influence in setting fmax for fast muscle fiber types.
Swank
Douglas M
DM
Department of Biology and Center for Biotechnology, Rensselaer Polytechnic Institute, Troy, New York 12180, USA. swankd@rpi.edu
Braddock
Joan
J
Brown
Waylon
W
Lesage
Heather
H
Bernstein
Sanford I
SI
Maughan
David W
DW
D000205:Actomyosin / Q000737:chemistry; D000251:Adenosine Triphosphatases / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D001665:Binding Sites; D001703:Biophysics / Q000379:methods*; D003433:Crosses, Genetic; D004330:Drosophila; D004548:Elasticity; D005091:Exons; D007700:Kinetics; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009068:Movement; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000473:pathology; D009132:Muscles / Q000378:metabolism; D009218:Myosins / Q000737:chemistry* / Q000648:ultrastructure; D009991:Oscillometry; D011487:Protein Conformation; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D019076:Transgenes; D014921:Wings, Animal / Q000378:metabolism
D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D000255:Adenosine Triphosphate; D000205:Actomyosin; D000251:Adenosine Triphosphatases; D009218:Myosins