Disrupting the Myosin Converter-Relay Interface Impairs Drosophila Indirect Flight Muscle Performance

Abstract

Structural interactions between the myosin converter and relay domains have been proposed to be critical for the myosin power stroke and muscle power generation. We tested this hypothesis by mutating converter residue 759, which interacts with relay residues I508, N509, and D511, to glutamate (R759E) and determined the effect on Drosophila indirect flight muscle mechanical performance. Work loop analysis of mutant R759E indirect flight muscle fibers revealed a 58% and 31% reduction in maximum power generation (P(WL)) and the frequency at which maximum power (f(WL)) is generated, respectively, compared to control fibers at 15 °C. Small amplitude sinusoidal analysis revealed a 30%, 36%, and 32% reduction in mutant elastic modulus, viscous modulus, and mechanical rate constant 2πb, respectively. From these results, we infer that the mutation reduces rates of transitions through work-producing cross-bridge states and/or force generation during strongly bound states. The reductions in muscle power output, stiffness, and kinetics were physiologically relevant, as mutant wing beat frequency and flight index decreased about 10% and 45% compared to control flies at both 15 °C and 25 °C. Thus, interactions between the relay loop and converter domain are critical for lever-arm and catalytic domain coordination, high muscle power generation, and optimal Drosophila flight performance.

Mapping Interactions between Myosin Relay and Converter Domains That Power Muscle Function

“…We previously demonstrated that converter mutation R759E disrupts biochemical, biophysical, mechanical, and ultrastructural properties of Drosophila muscle myosin and indirect flight muscles (20,21 1 and Ref. 22).…”

“…The R759E mutation also disrupts flight ability, reduces myofibril stability, and diminishes muscle fiber power generation (20,21). Our molecular modeling studies identified specific residues in the relay domain (Asn 509 and Asp 511 ) that are likely to interact with converter domain residue Arg 759 during the pre-and postpower stroke states (22).…”

“…Residue Arg 759 and Residues in the Relay Domain-Mutation R759E in the myosin converter domain results in biochemical and biophysical defects as well as aberrant muscle structural and physiological properties (20,21). The central portion of the converter domain is encoded by exon 11e in indirect flight muscle (Fig.…”

An embryonic myosin converter domain influences Drosophila indirect flight muscle stretch activation, power generation and flight

“…At pCa 5.0, a 1% ML step stretch over 0.5 ms, the fastest rate that can be applied on our mechanics apparatus, and 3.5 ms, an estimated lengthening rate for Drosophila IFM during flight (Swank et al, 2006a;Wang et al, 2011), were applied to the fibers at 15°C. Our work loop measurements and previous work have shown that 1% ML is optimal for wild-type power generation in the fly (Ramanath et al, 2011;Wang et al, 2011). After holding the fiber at the new length for 300 ms, the fibers were slowly, over 500 ms, returned to their original length.…”

A mutation in the converter subdomain of Aspergillus nidulans MyoB blocks constriction of the actomyosin ring in cytokinesis

“…Essential to this role is the converter's ability to form bonds to a helical extension of the L50 subdomain of the head termed the relay helix (Kronert et al, 2014;Ramanath et al, 2011), and the residues mediating this interaction are among the most highly conserved within the myosin superfamily (Dominguez et al, 1998). Of eight converter residues that have been shown to participate in the converter/relay interaction during the ATP hydrolysis cycle (Dominguez et al, 1998;Houdusse et al, 1999;Kronert et al, 2014;Yu et al, 2007), six lie in the immediate vicinity of the G843D mutation.…”