Leishmania donovani ADF/cofilin (LdCof) is a novel member of ADF/cofilin family. LdCof depolymerizes, but does not co-sediment with, rabbit muscle actin filaments. Its F-actin depolymerizing activity is pH independent. Further, it possesses weak F-actin severing activity. In order to better understand its characteristic properties, we have determined the solution NMR structure of LdCof and have analyzed protein backbone dynamics from N-15-relaxation measurements. The structure of LdCof possesses a conserved ADF/cofilin fold with a central mixed beta-sheet consisting of six beta-strands which is surrounded by five a-helices. LdCof structure has conserved G/F-actin binding site which includes the characteristic long kinked alpha-helix (alpha 3). LdCof binds to rabbit muscle ADP-G-actin with 1:1 stoichiometry (K-d similar to 0.2 mu M). The F-actin binding site is not well formed and analysis of N-15-relaxation data shows that residues in the beta 4-beta 5 loop region and C-terminal are relatively flexible, which seems to be a determinant for the low F-actin severing activity of LdCof. (C) 2010 Elsevier Inc. All rights reserved.