Novel Myosin Associated Proteins

Abstract

A synchronous insect flight muscle (IFM) relies on high frequency operation to achieve higher power output than a comparable synchronous muscle. The biochemical, ultrastructural, and mechanical adaptations that define the performance of this muscle type are not completely understood. IFM is characterized by its high stiffness, a property that influences the magnitude of stretch activation and ability to deliver high power to the wings. IFM is also characterized by the presence of unique (novel) myofibrillar proteins, and atypical modifications of conventional proteins, that likely affect the functional properties of this muscle. Here we review the properties of three thick filament associated proteins that may be important in stabilizing the myofilament lattice and impart rigidity to the myofibril. Drosophila flightin is an ∼20 kDa myosin rod binding protein found exclusively in IFM that exists as two unphosphorylated and nine phosphorylated isovariants in adult muscle. Genetic analyses have shown that flightin is essential for IFM development, structural integrity and function. Zeelins are found in Lethocerus leg (zeelin 1) and flight muscle (zeelin 1 and zeelin 2). Although the exact role of zeelins is not known, it has been speculated that they play a role in maintaining the structural organization of the thick filament and the regularity of the myofilament lattice. Stretchin-MLCK is a conceptual Drosophila protein that has been studied through the virtual translation of its coding region. The transcription unit is hypothesized to express seven different transcripts. None of the conceptual protein products have been shown to be expressed in IFM, although preliminary studies have identified a protein that may correspond to one of the small kinase isoforms and a second, kettin-like isoform that does not correspond to any of the predicted products.