title: CacyBP/SIP as a novel modulator of the thin filament.
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.
authors.affiliation: Nencki Institute of Experimental Biology, 02-093 Warsaw, Poland.
authors.forename: Ewelina
authors.initials: E
authors.lastname: Jurewicz
authors.forename: Zofia
authors.initials: Z
authors.lastname: Ostrowska
authors.forename: Jolanta
authors.initials: J
authors.lastname: Jozwiak
authors.forename: Maria Jolanta
authors.initials: MJ
authors.lastname: Redowicz
authors.forename: Wieslawa
authors.initials: W
authors.lastname: Lesniak
authors.forename: Joanna
authors.initials: J
authors.lastname: Moraczewska
authors.forename: Anna
authors.initials: A
authors.lastname: Filipek
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002645:Chickens; D002846:Chromatography, Affinity; D005455:Fluorescent Antibody Technique; D007124:Immunoenzyme Techniques; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008854:Microscopy, Electron; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism*; D051381:Rats; D014335:Tropomyosin / Q000378:metabolism*
chemical_list: D000199:Actins; C491777:CacyBP protein, rat; D002135:Calcium-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D015879:Myosin Subfragments; D014335:Tropomyosin; D002118:Calcium