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CacyBP/SIP as a novel modulator of the thin filament.

Authors :: Jurewicz E
Ostrowska Z
Jozwiak J
Redowicz MJ
Lesniak W
Moraczewska J
Filipek A
Source :: Biochimica et biophysica acta [Biochim Biophys Acta] 2013 Mar; Vol. 1833 (3), pp. 761-6. Date of Electronic Publication: 2012 Dec 22.
Publication Year :: 2013
Abstract: The CacyBP/SIP protein interacts with several targets, including actin. Since the majority of actin filaments are associated with tropomyosin, in this work we characterized binding of CacyBP/SIP to the actin-tropomyosin complex and examined the effects of CacyBP/SIP on actin filament functions. By using reconstituted filaments composed of actin and AEDANS-labeled tropomyosin, we observed that binding of CacyBP/SIP caused an increase in tropomyosin fluorescence intensity indicating the occurrence of conformational changes within the filament. We also found that CacyBP/SIP bound directly to tropomyosin and that these proteins did not compete with each other for binding to actin. Electron microscopy showed that in the absence of tropomyosin CacyBP/SIP destabilized actin filaments, but tropomyosin reversed this effect. Actin-activated myosin S1 ATPase activity assays, performed using a colorimetric method, indicated that CacyBP/SIP reduced ATPase activity and that the presence of tropomyosin enhanced this inhibitory effect. Thus, our results suggest that CacyBP/SIP, through its interaction with both actin and tropomyosin, regulates the organization and functional properties of the thin filament.<br /> (Copyright © 2012 Elsevier B.V. All rights reserved.)