The major cytoskeletal protein of most cells is actin, which polymerizes to form actin filaments (F-actin).Each actin monomer (G-actin) contains a divalent alkaline earth metal ion (in vivo Mg2+;in vitro usually Ca2+) as a cofactor that is crucial for protein polymerization.Prior to this study, however, whether or not other types of metal ions also can occur in actin to play the same role as Mg2+ or Ca2+ remains unclear.Herein, we report a new class actin from the gills or mantles of oyster (AGO) Crassostrea gigas, a well-known zinc-enriched source.