43rd ANNUAL DROSOPHILA RESEARCH CONFERENCE
April 10-14, 2002

PROGRAM AND ABSTRACT VOLUME
Workshop Abstract

18W
Alternative N-terminal regions of Drosophila Myosin heavy chain tune cross-bridge kinetics for optimal muscle power output. Douglas M. Swank, Sanford I. Bernstein, David W. Maughan. Department of Biology and Molecular Biology Institute, San Diego State University, CA, and Department of Molecular Physiology and Biophysics, University of Vermont, Burlington.

Two alternative choices exist for a region of Drosophila myosin heavy chain (MHC) located near the N-terminus (residues 69-116 of chicken skeletal MHC). This region, encoded by exons 3a and 3b, is one of only four variable domains in the S-1 head. To test whether this region plays a role in setting myosin and muscle functional abilities, we performed sinusoidal analysis on indirect flight muscle (IFM) fibers isolated from Drosophila expressing either EMB-3b or IFI-3a (two myosin chimeras made by exchanging the exon 3 region between two myosin isoforms: EMB, an embryonic isoform and IFI, the native IFM isoform). Previously, we showed 4- and 7-fold higher maximum power generation (P_max) and optimal frequency of power generation (f_max), respectively, in IFM fibers expressing IFI compared to EMB. The exon 3 region contributes significantly to these differences. EMB-3b increased P_max and f_max 2-fold compared to EMB, while IFI-3a decreased P_max and f_max to 80% of IFI values. Surprisingly, IFI-3a Drosophila fly, although not as well as IFI. To fly at 15^oC, IFI-3a flies increased flight muscle power generation by decreasing wing beat frequency to 124 ± 3.6 Hz, equal to their IFM's f_max. Thus exon 3 is important for tuning myosin kinetics to match muscle speed during locomotion.