A Comparative Structural Analysis of the ADF/Cofilin Family

Actin-depolymerizing factor (ADF) and cofilin define a family of actin-binding proteins essential for the rapid turnover of filamentous actin in vivo. Here we present the 2.0 A crystal structure of Arabidopsis thaliana ADF1 (AtADF1), the first plant crystal structure from the ADF/cofilin (AC) family. Superposition of the four AC isoform struc- tures permits an accurate sequence alignment that differs from previously reported data for the loca- tion of vertebrate-specific inserts and reveals a contiguous, vertebrate-specific surface opposite the putative actin-binding surface. Extending the struc- ture-based sequence alignment to include 30 addi- tional isoforms indicates three major groups: verte- brates, plants, and "other eukaryotes." Within these groups, several structurally conserved residues that are not conserved throughout the entire AC family have been identified. Residues that are highly con- served among all isoforms tend to cluster around the tryptophan at position 90 and a structurally conserved kink in a-helix 3. Analysis of surface character shows the presence of a hydrophobic patch and a highly conserved acidic cluster, both of which include several residues previously impli- cated in actin binding. Proteins 2000;41:374 -384.