Domain analysis of the actin-binding and actin-remodeling activities of drebrin. 
Drebrin is an actin-binding protein which is expressed at highly levels in neurons.  When introduced into fibroblasts, it has been known to bind to F-actin and to cause remodeling of F-actin.  Here, we performed a domain analysis of the actin-binding and actin-remodeling activities of drebrin.  Various fragments of drebrin cDNA were fused with green fluorescent protein cDNA and introduced into Chinese hamster ovary cells.  Association of the fusion protein with F-actin and remodeling of the F-actin were examined.  We found that the central 85-amino-acid sequence (residues 233-317) was sufficient for the binding to and remodeling of F-actin.  The binding activity of this fragment was relatively low compared with that of full-length drebrin, but all the types of abnormalities of F-actin that are observed with full-length drebrin were also observed with this fragment.  When this sequence was further fragmented, the actin-binding activity was greatly reduced and the actin-remodeling activity disappeared.  The actin-binding activity of the central region of drebrin was confirmed by a cosedimentation assay of chymotryptic fragments of drebrin with purified actin.  These data indicate that the actin-binding domain and actin-remodeling domain are identical and that this domain is located at the central region of drebrin.