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Alternative exon 9-encoded relay domains affect more than one communication pathway in the Drosophila myosin head.

ABSTRACT: We investigated the biochemical and biophysical properties of one of the four alternative regions within the Drosophila myosin catalytic domain: the relay domain encoded by exon 9. This domain of the myosin head transmits conformational changes in the nucleotide-binding pocket to the converter domain, which is crucial to coupling catalytic activity with mechanical movement of the lever arm. To study the function of this region, we used chimeric myosins (IFI-9b and EMB-9a), which were generated by exchange of the exon 9-encoded domains between the native embryonic body wall (EMB) and indirect flight muscle isoforms (IFI). Kinetic measurements show that exchange of the exon 9-encoded region alters the kinetic properties of the myosin S1 head. This is reflected in reduced values for ATP-induced actomyosin dissociation rate constant (K(1)k(+2)) and ADP affinity (K(AD)), measured for the chimeric constructs IFI-9b and EMB-9a, compared to wild-type IFI and EMB values. Homology models indicate that, in addition to affecting the communication pathway between the nucleotide-binding pocket and the converter domain, exchange of the relay domains between IFI and EMB affects the communication pathway between the nucleotide-binding pocket and the actin-binding site in the lower 50-kDa domain (loop 2). These results suggest an important role of the relay domain in the regulation of actomyosin cross-bridge kinetics.

SUBMITTER: Bloemink MJ

PROVIDER: S-EPMC3119900 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature

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Alternative exon 9-encoded relay domains affect more than one communication pathway in the Drosophila myosin head.

Bloemink Marieke J MJ Dambacher Corey M CM Knowles Aileen F AF Melkani Girish C GC Geeves Michael A MA Bernstein Sanford I SI

Journal of molecular biology 20090422 4

We investigated the biochemical and biophysical properties of one of the four alternative regions within the Drosophila myosin catalytic domain: the relay domain encoded by exon 9. This domain of the myosin head transmits conformational changes in the nucleotide-binding pocket to the converter domain, which is crucial to coupling catalytic activity with mechanical movement of the lever arm. To study the function of this region, we used chimeric myosins (IFI-9b and EMB-9a), which were generated b ...[more]

PMID: 19393244

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Project description:Muscle myosin heavy chain (MHC) rod domains intertwine to form alpha-helical coiled-coil dimers; these subsequently multimerize into thick filaments via electrostatic interactions. The subfragment 2/light meromyosin "hinge" region of the MHC rod, located in the C-terminal third of heavy meromyosin, may form a less stable coiled-coil than flanking regions. Partial "melting" of this region has been proposed to result in a helix to random-coil transition. A portion of the Drosophila melanogaster MHC hinge is encoded by mutually exclusive alternative exons 15a and 15b, the use of which correlates with fast (hinge A) or slow (hinge B) muscle physiological properties. To test the functional significance of alternative hinge regions, we constructed transgenic fly lines in which fast muscle isovariant hinge A was switched for slow muscle hinge B in the MHC isoforms of indirect flight and jump muscles. Substitution of the slow muscle hinge B impaired flight ability, increased sarcomere lengths by approximately 13% and resulted in minor disruption to indirect flight muscle sarcomeric structure compared with a transgenic control. With age, residual flight ability decreased rapidly and myofibrils developed peripheral defects. Computational analysis indicates that hinge B has a greater coiled-coil propensity and thus reduced flexibility compared to hinge A. Intriguingly, the MHC rod with hinge B was approximately 5 nm longer than myosin with hinge A, consistent with the more rigid coiled-coil conformation predicted for hinge B. Our study demonstrates that hinge B cannot functionally substitute for hinge A in fast muscle types, likely as a result of differences in the molecular structure of the rod, subtle changes in myofibril structure and decreased ability to maintain sarcomere structure in indirect flight muscle myofibrils. Thus, alternative hinges are important in dictating the distinct functional properties of myosin isoforms and the muscles in which they are expressed.

Dataset Information

Alternative exon 9-encoded relay domains affect more than one communication pathway in the Drosophila myosin head.

Publications

Alternative exon 9-encoded relay domains affect more than one communication pathway in the Drosophila myosin head.

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