Tropomyosins, a family of actin-binding regulatory proteins, are present in muscle and non-muscle cells. Multiple tropomyosin (TM) isoforms differ in actin affinity and regulatory properties, but little is known about the molecular bases of these differences. The C-terminus of actin stabilizes contacts between actin subunits in the filament and interacts with myosin and regulatory proteins. The goal of this work was to reveal how structural changes in actin and differences between TM isoforms affect binding between these proteins and affect thin filament regulation. Actin proteolytically truncated by three C-terminal amino acids exhibited 1.2-1.5 fold reduced affinity for non-muscle and smooth muscle tropomyosin isoforms. The truncation increased the cooperativity of myosin S1-induced tropomyosin binding for short tropomyosins (TM5a and TM1b9a), but it was neutral for long isoforms (smTM and TM2). Actin modification affected regulation of actomyosin ATPase activity in the presence of all tropomyosins by shifting the filament into a more active state. We conclude that the integrity of the actin C-terminus is important for actin-tropomyosin interactions, however the increased affinity of tropomyosin binding in the S1-induced state of the filament appears not to be involved in the tropomyrosin isoform-dependent mechanism of the actomyosin ATPase activation. (C) 2008 Elsevier B.V. All rights reserved.
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Nagoya Univ, Grad Sch Sci, Nagoya, Aichi 4648602, JapanNagoya Univ, Grad Sch Sci, Nagoya, Aichi 4648602, Japan
Takeda, Shuichi
Koike, Ryotaro
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Nagoya Univ, Grad Sch Informat, Nagoya, Aichi 4648601, JapanNagoya Univ, Grad Sch Sci, Nagoya, Aichi 4648602, Japan
Koike, Ryotaro
Fujiwara, Ikuko
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Osaka City Univ, Grad Sch Sci, Osaka, Osaka 5588585, JapanNagoya Univ, Grad Sch Sci, Nagoya, Aichi 4648602, Japan
Fujiwara, Ikuko
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Narita, Akihiro
Miyata, Makoto
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Osaka City Univ, Grad Sch Sci, Osaka, Osaka 5588585, Japan
Osaka City Univ, OCU Adv Res Inst Nat Sci & Technol OCARINA, Osaka, Osaka 5588585, JapanNagoya Univ, Grad Sch Sci, Nagoya, Aichi 4648602, Japan
Miyata, Makoto
Ota, Motonori
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Nagoya Univ, Grad Sch Informat, Nagoya, Aichi 4648601, JapanNagoya Univ, Grad Sch Sci, Nagoya, Aichi 4648602, Japan
Ota, Motonori
Maeda, Yuichiro
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Nagoya Univ, Grad Sch Informat, Nagoya, Aichi 4648601, JapanNagoya Univ, Grad Sch Sci, Nagoya, Aichi 4648602, Japan