Functional analysis of mammalian actin regulatory proteins, cofilin and destrin

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Cofilin and destrin, low molecular weight actin-binding proteins, are related to each other. Cofilin depolymerizes F-actin in a pH- dependent manner, while destrin does in a pH-independent manner. We have found that the Trp^<104>-Met^<115> region of cofilin (and destrin) is an actin binding site, and that this region is a polyphosphoinositide-binding site. The synthetic dodecapeptide patterned on the sequence corresponding to this region binds to PIP2 (PIP) as well as actin tightly, and thus is a PIP2 (PIP)-sensitive inhibitor of actin polymerization. We have further found that cofilin and the dodecapeptide inhibit PIP2 hydrolysis catalyzed by phospholipase C. Therefore, cofilin may function not only as a regulator of actin cytoskeleton but also as a regulator of the phosphoinositide signaling pathway.A cofilin-like protein has been identified from budding yeast. We carried out molecular cloning of this protein. We then expressed and purified a recombinant form of this protein, and characterized the recombinant protein. The results have shown that the protein depolymerizes F-actin in a pH-dependent manner, binds to both F- and G- actin, and binds to PIP2. These characteristics of the protein are completely the same as those of mammalian cofilin. Thus, we named this protein COF1. COF1 is found to be essential for yeast cell growth.