Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 282, Issue 8, Pages 5871-5879Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M609850200
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Funding
- NHLBI NIH HHS [T32 HL007873] Funding Source: Medline
- NIGMS NIH HHS [GM067246, R01 GM038542, R01 GM038542-20, GM38542, R01 GM067246] Funding Source: Medline
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The heterodimeric actin-capping protein (CP) can be inhibited by polyphosphoinositides, which may be important for actin polymerization at membranes in cells. Here, we have identified a conserved set of basic residues on the surface of CP that are important for the interaction with phosphaticlylinositol 4,5-bisphosphate (PIP2). Computational docking studies predicted the identity of residues involved in this interaction, and functional and physical assays with site-directed mutants of CP confirmed the prediction. The PIP2 binding site overlaps with the more important of the two known actin-binding sites of CP. Correspondingly, we observed that loss of PIP2 binding correlated with loss of actin binding among the mutants. Using TIRF (total internal reflection fluorescence) microscopy, we observed that PIP2 rapidly converted capped actin filaments to a growing state, consistent with uncapping. Together, these results extend our understanding of how CP binds to the barbed end of the actin filament, and they support the idea that CP can wobble when bound to the barbed end solely by the C-terminal tentacle of its beta-subunit.
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