Interaction of S100a(0) protein with the actin capping protein, CapZ: Characterization of a putative S100a(0) binding site in CapZ alpha-subunit

S100a(0), a Ca2+-binding protein expressed predominantly in cardiac and skeletal muscle tissues, was demonstrated by chemical cross-linking to interact in a Ca2+-dependent manner with the actin capping protein CapZ. TRTK-12, a peptide contained within the COOH-terminal region of CapZ alpha, inhibited S100a,: CapZ interaction in a dose-dependent manner. TRTK-12 was shown by cross-linking to bind S100a(0) in the presence of Ca2+, and by fluorescence spectrophotometry to interact in a saturable manner with the anionic phospholipid and a regulator of CapZ activity, phosphatidylinositol 4-monophosphate; but not with the neutral phospholipid, phosphatidylcholine. These data suggest S100a(0) and polyphosphoinositides bind to the same COOH-terminal region of CapZ alpha, thus potentially modulating CapZ activity. (C) 1996 Academic Press, Inc.