Changes in myofibrillar structure and function produced by N-terminal deletion of the regulatory light chain in Drosophila.
The similarity of amino acid sequence and motifs of the N-terminal extensions of certain class II myosin light chains, found throughout the animal kingdom, suggest a common functional role. One possible role of the N-terminal extension is to enhance oscillatory work and power production in striated muscles that normally operate in an oscillatory mode. We conducted small-angle X-ray diffraction experiments and small-length-perturbation analysis to examine the structural and functional consequences of deleting the N-terminal extension of the myosin regulatory light chain (RLC) in Drosophila flight muscle. The in vivo lattice spacing of dorsal longitudinal muscle (DLM) of flies lacking the RLC N-terminal extension (Dmlc2delta2-46) was approximately 1 nm less than that of wild type (48.56 +/- 0.02 nm). The myofilament lattice of detergent-treated, demembranated DLM swelled, with the DmlcdeltaA2-46 lattice expanding more than wild type and requiring roughly twice the concentration of Dextran T500 to restore its lattice to in vivo spacing (9-10% vs. 4% w/v). The calcium sensitivity and maximum amplitude of net oscillatory work near the in vivo lattice spacing was significantly lower in Dmlc2delta2-46 compared to wild type (pCa50 shifted by approximately one-third of a pCa unit; amplitude reduced by approximately one-half). These changes were in contrast to the lack of effect reported in a previous study carried out in the absence of Dextran T500. The results are consistent with the N-terminal extension interacting with actin to increase the probability that crossbridges form during stretch-activated oscillatory work and power production, especially at submaximal levels of calcium activation.
Irving
T
T
Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology, Chicago 60616, USA.
Bhattacharya
S
S
Tesic
I
I
Moore
J
J
Farman
G
G
Simcox
A
A
Vigoreaux
J
J
Maughan
D
D
D000818:Animals; D002118:Calcium / Q000378:metabolism; D024722:Cardiac Myosins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D003911:Dextrans / Q000494:pharmacology; D004330:Drosophila; D017353:Gene Deletion; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009210:Myofibrils / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D018994:Myosin Light Chains / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010952:Plasma Substitutes / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D014961:X-Ray Diffraction
D003911:Dextrans; D018994:Myosin Light Chains; D010952:Plasma Substitutes; C107184:myosin light chain 2; D024722:Cardiac Myosins; D002118:Calcium