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Curr Biol. 2010 May 11;20(9):861-7. doi: 10.1016/j.cub.2010.03.026. Epub 2010 Apr 1.

GMF is a cofilin homolog that binds Arp2/3 complex to stimulate filament debranching and inhibit actin nucleation.

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Department of Biology and Rosenstiel Basic Medical Science Research Center, Brandeis University, 415 South Street, Waltham, MA 02454, USA.


Cell locomotion and endocytosis are powered by the rapid polymerization and turnover of branched actin filament networks nucleated by Arp2/3 complex. Although a large number of cellular factors have been identified that stimulate Arp2/3 complex-mediated actin nucleation, only a small number of studies so far have addressed which factors promote actin network debranching. Here, we investigated the function of a conserved homolog of ADF/cofilin, glia maturation factor (GMF). We found that S. cerevisiae GMF (also called Aim7) localizes in vivo to cortical actin patches and displays synthetic genetic interactions with ADF/cofilin. However, GMF lacks detectable actin binding or severing activity and instead binds tightly to Arp2/3 complex. Using in vitro evanescent wave microscopy, we demonstrated that GMF potently stimulates debranching of actin filaments produced by Arp2/3 complex. Further, GMF inhibits nucleation of new daughter filaments. Together, these data suggest that GMF binds Arp2/3 complex to both "prune" daughter filaments at the branch points and inhibit new actin assembly. These activities and its genetic interaction with ADF/cofilin support a role for GMF in promoting the remodeling and/or disassembly of branched networks. Therefore, ADF/cofilin and GMF, members of the same superfamily, appear to have evolved to interact with actin and actin-related proteins, respectively, and to make mechanistically distinct contributions to the remodeling of cortical actin structures.

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