It has been previously reported that phosphorylated cofilin interacted with 14-3-3ζ protein to generate a sub-micromolar K(d) binary complex. Here we challenge this hypothesis by analyzing the direct association of recombinant cofilin with 14-3-3ζ using different in vitro biochemical methods. Phosphorylated cofilin at high concentration binds to 14-3-3 immobilized on nitrocellulose, however no complex formation was detected by means of native gel electrophoresis or chemical crosslinking. Intact dimeric or mutant monomeric 14-3-3 was unable to form stable complexes with phosphorylated or unphosphorylated cofilin detected by size-exclusion chromatography. In co-sedimentation assay 14-3-3 did not affect interaction of cofilin with F-actin. The data of native gel electrophoresis indicate that 14-3-3 did not affect interaction of cofilin with G-actin. Thus, cofilin only weakly interacts with 14-3-3 and therefore cannot directly compete with phosphorylated small heat shock protein HspB6 for its binding to 14-3-3. It is hypothesized that phosphorylated HspB6 might affect interaction of 14-3-3 with protein phosphatases (and/or protein kinases) involved in dephosphorylation (or phosphorylation) of cofilin and by this means regulate cofilin-dependent reorganization of cytoskeleton.
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