A comparative structural analysis of the ADF/cofilin family

Actin-depolymerizing factor (ADF) and cofilin define a family of actin-bind ing proteins essential for the rapid turnover of filamentous actin in vivo. Here we present the 2.0 Angstrom crystal structure of Arabidopsis thaliana ADF1 (AtADF1), the first plant crystal structure from the ADF/cofilin (AC) family. Superposition of the four AC isoform structures permits an accurat e sequence alignment that differs from previously reported data for the loc ation. of vertebrate-specific inserts and reveals a contiguous, vertebrate- specific surface opposite the putative actin-binding surface. Extending the structure-based sequence alignment to include 30 additional isoforms indic ates three major groups: vertebrates, plants, and "other eukaryotes." Withi n these groups, several structurally conserved residues that are not conser ved throughout the entire AC family have been identified. Residues that are highly conserved among all isoforms tend to cluster around the tryptophan at position 90 and a structurally conserved kink in alpha -helix 3. Analysi s of surface character shows the presence of a hydrophobic patch and a high ly conserved acidic cluster, both of which include several residues previou sly implicated in actin binding. (C) 2000 Wiley-Liss, Inc.