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    CacyBP/SIP as a novel modulator of the thin filament

    Year: 2013

    Journal: Biochimica et Biophysica Acta (BBA) - Molecular Cell Research Volume 1833, Issue 3, March 2013, Pages 761–766, 20130402

    Authors: Ewelina Jurewicz 1, Zofia Ostrowska 2, Jolanta Jozwiak 1, Maria Jolanta Redowicz 1, Wieslawa Lesniak 1, Joanna Moraczewska 2, Anna Filipek 1

    Last authors: Anna Filipek

    Organizations: 1 Nencki Institute of Experimental Biology, 3 Pasteur Street, 02-093 Warsaw, Poland 2 Kazimierz Wielki University, 30 Chodkiewicz Street, 85-064 Bydgoszcz, Poland

    Country: Poland

    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.