Variable N-terminal regions of muscle myosin heavy chain modulate ATPase rate and actin sliding velocity.
We integratively assessed the function of alternative versions of a region near the N terminus of Drosophila muscle myosin heavy chain (encoded by exon 3a or 3b). We exchanged the alternative exon 3 regions between an embryonic isoform and the indirect flight muscle isoform. Each chimeric myosin was expressed in Drosophila indirect flight muscle, in the absence of other myosin isoforms, allowing for purified protein analysis and whole organism locomotory studies. The flight muscle isoform generates higher in vitro actin sliding velocity and solution ATPase rates than the embryonic isoform. Exchanging the embryonic exon 3 region into the flight muscle isoform decreased ATPase rates to embryonic levels but did not affect actin sliding velocity or flight muscle ultrastructure. Interestingly, this swap only slightly impaired flight ability. Exchanging the flight muscle-specific exon 3 region into the embryonic isoform increased actin sliding velocity 3-fold and improved indirect flight muscle ultrastructure integrity but failed to rescue the flightless phenotype of flies expressing embryonic myosin. These results suggest that the two structural versions of the exon 3 domain independently influence the kinetics of at least two steps of the actomyosin cross-bridge cycle.
Swank
Douglas M
DM
Biology Department and Molecular Biology Institute, San Diego State University, San Diego, California 92182-4614, USA. dswank@sunstroke.sdsu.edu
Knowles
Aileen F
AF
Kronert
William A
WA
Suggs
Jennifer A
JA
Morrill
George E
GE
Nikkhoy
Massoud
M
Manipon
Gracielle G
GG
Bernstein
Sanford I
SI
D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D004330:Drosophila; D020409:Molecular Motor Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D017421:Sequence Analysis
D000199:Actins; D020409:Molecular Motor Proteins; D000251:Adenosine Triphosphatases; D018995:Myosin Heavy Chains