The N-terminal extension and phosphorylation of the myosin regulatory light chain (RLC) independently improve Drosophila melanogaster flight performance. Here we examine the functional and structural role of the RLC in chemically :skinned fibers at various thick and thin filament lattice spacings from four transgenic Drosophila lines: rescued null or control (Dmlc(2+)), truncated N-terminal extension (Dmlc2(Delta 2-46)), disrupted myosin light chain kinase phosphorylation sites (Dmlc2(S66A,S67A)) and dual mutant (Dmlc2(Delta 2-46); (S66A,S67A)) The N-terminal extension truncation and phosphorylation sites disruption mutations decreased oscillatory power output and the frequency of maximum power output in maximally Ca2+-activated fibers compressed to near in vivo inter-thick filament spacing, with the phosphorylation sites disruption mutation having a larger affect. The diminished power output parameters with the N-terminal extension truncation and phosphorylation sites disruption mutations were due to the reduction of the number of strongly-bound cross-bridges and rate of myosin force producion, with the larger parameter reductions in the phosphorylation sites disruption mutation additionally related to reduced myosin attachment time. The phosphorylation and N-terminal extension-dependent boost in cross-bridge kinetics corroborates previous structural data, which indicate these RLC attributes play a complementary role in moving and orienting myosin heads toward actin target sites, thereby increasing fiber and whole fly power generation.
Miller, M. S., Farman, G. P., Braddock, J. M., Soto-Adames, F. N., Irving, T. C., Vigoreaux, J. O., & Maughan, D. W. (2011). Regulatory light chain phosphorylation and N-terminal extension increase cross-bridge binding and power output in Drosophila at in vivo myofilament lattice spacing. Biophysical journal, 100(7), 1737--1746. https://doi.org/10.1016/j.bpj.2011.02.028