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Author Notes:

Address correspondence to: Shoichiro Ono ( sono@emory.edu)

Present address: Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.

We thank Belinda Bullard and Taylor Allen for communicating studies on C. elegans kettin and helpful discussion; Sumiko Kimura for helpful discussion; Guy Benian for comments on the manuscript; Henry Epstein for anti-myoA antibody; Gary Moulder and Robert Barstead for an α-actinin mutant; and Pamela Hoppe for MH24, MH40, and MH44. Some C. elegans strains were provided by the Caenorhabditis Genetics Center, which is funded by the National Institute of Health National Center for Research Resources.

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Research Funding:

This work was supported by National Institutes of Health Grant R01 AR48615 (to S. O.).

Caenorhabditis elegans Kettin, a Large Immunoglobulin-like Repeat Protein, Binds to Filamentous Actin and Provides Mechanical Stability to the Contractile Apparatuses in Body Wall Muscle

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Journal Title:

Molecular Biology of the Cell

Volume:

Volume 17, Number 6

Publisher:

, Pages 2722-2734

Type of Work:

Article | Final Publisher PDF

Abstract:

Kettin is a large actin-binding protein with immunoglobulin-like (Ig) repeats, which is associated with the thin filaments in arthropod muscles. Here, we report identification and functional characterization of kettin in the nematode Caenorhabditis elegans. We found that one of the monoclonal antibodies that were raised against C. elegans muscle proteins specifically reacts with kettin (Ce-kettin). We determined the entire cDNA sequence of Ce-kettin that encodes a protein of 472 kDa with 31 Ig repeats. Arthropod kettins are splice variants of much larger connectin/titin-related proteins. However, the gene for Ce-kettin is independent of other connectin/titin-related genes. Ce-kettin localizes to the thin filaments near the dense bodies in both striated and nonstriated muscles. The C-terminal four Ig repeats and the adjacent non-Ig region synergistically bind to actin filaments in vitro. RNA interference of Ce-kettin caused weak disorganization of the actin filaments in body wall muscle. This phenotype was suppressed by inhibiting muscle contraction by a myosin mutation, but it was enhanced by tetramisole-induced hypercontraction. Furthermore, Ce-kettin was involved in organizing the cytoplasmic portion of the dense bodies in cooperation with α-actinin. These results suggest that kettin is an important regulator of myofibrillar organization and provides mechanical stability to the myofibrils during contraction.

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© 2006 by The American Society for Cell Biology

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