The Two Caenorhabditis elegans Actin-Depolymerizing Factor/Cofilin Proteins Differently Enhance Actin Filament Severing and Depolymerization

摘要

Actin-depolymerizing factor (ADF)/cofilin enhances the turnover of actin filaments by two separable activities: filament severing and pointed-end depolymerization.Multicellular organisms express multiple ADF/cofilin isoforms in a tissue-specific manner,and the vertebrate proteins are grouped into ADFs and cofilins on the basis of their biochemical activity.A recent comparative study has shown that ADF has greater severing and depolymerizing activities than cofilin [Chen,H.,Bernstein,B.W.,Sneider,J.M.,Boyle,J.A.,Minamide,L.S.,and Bamburg,J.R.(2004) Biochemistry 43,7127-7142].Here,we show that the two Caenorhabditis elegans ADF/cofilin isoforms exhibit different activities for severing and depolymerizing actin filaments.The ADF-like non-muscle isoform UNC-60A had greater activities to cause net depolymerization and inhibit polymerization than the cofilin-like muscle isoform UNC-60B.Surprisingly,UNC-60B exhibited much stronger severing activity than UNC-60A,which was the opposite of what was observed for vertebrate counterparts.Moreover,UNC-60B induced much faster pointed-end depolymerization of rabbit muscle actin than UNC-60A,while UNC-60A caused slightly faster depolymerization of C.elegans actin than UNC-60B.These results suggest that cofilin-like UNC-60B is kinetically more efficient in enhancing actin turnover than ADF-like UNC-60A,while ADF-like UNC-60A is suitable for maintaining higher concentrations of monomeric actin.These functional differences might be specifically adapted for different actin dynamics in muscle and non-muscle cells.