Catch muscle of bivalve molluscs contains myosin- and twitchin-associated protein kinase phosphorylating myorod |
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Authors: | Oleg S Matusovsky Nikolay S Shelud'ko Tatyana V Permyakova Magdalena Zukowska Apolinary Sobieszek |
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Institution: | 1. Institute for Biomedical Aging Research, Life Science Center, Austrian Academy of Sciences, Innsbruck, Austria;2. A.V. Zhirmunsky Institute of Marine Biology, Far East Branch of the Russian Academy of Sciences, Vladivostok, Russia |
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Abstract: | We have shown previously that myorod, a molluscan thick filament protein of unknown function, is phosphorylated by vertebrate smooth myosin light chain kinase (MLCK) in N-terminal unique region. The aim of the present study was to clarify whether such phosphorylation may occur in molluscan muscles. We detected three kinases endogenous to molluscan catch muscle, namely, to the complex of surface thick filament proteins that consists of twitchin, myosin, and myorod. The first kinase was a protein kinase A because it was inhibited by a specific inhibitor; the second one was associated with twitchin and phosphorylated myorod at its N-terminal unique region independently of Ca2+; and the third kinase was bound to myosin and phosphorylated myorod as well as myosin in the C-terminal part of both proteins. The myosin-associated kinase was inhibited by micromolar concentration of calcium ions. This enzyme could be separated from myosin by chromatography, whereas the kinase associated with twitchin could not be separated from twitchin. Since twitchin has a MLCK-like domain, it is possible that this domain was responsible for myorod phosphorylation. Phosphorylation of myorod within the twitchin–myosin–myorod complex increased the actin-activated Mg2+-ATPase activity of myosin. Taken together, these results indicate that phosphorylation of myorod by kinases associated with key proteins of catch contraction may contribute to the functional activity of myorod in molluscan smooth muscle. |
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Keywords: | MLCK myosin light chain kinase PKA cAMP-dependent protein kinase TW&ndash MY&ndash MR a complex of surface proteins from molluscan thick filaments fraction composed of twitchin myosin and myorod TW&ndash MR a complex of twitchin and myorod MHC myosin heavy chains |
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