Crystal structure of human V-1 in the apo form.

V-1, also known as myotrophin, is a 13 kDa ankyrin-repeat protein that binds and inhibits the heterodimeric actin capping protein (CP), which is a key regulator of cytoskeletal actin dynamics. The crystal structure of V-1 in complex with CP revealed that V-1 recognizes CP via residues spanning several ankyrin repeats. Here, the crystal structure of human V-1 is reported in the absence of the specific ligand at 2.3 A resolution. In the asymmetric unit, the crystal contains two V-1 monomers that exhibit nearly identical structures (Cα r.m.s.d. of 0.47 A). The overall structures of the two apo V-1 chains are also highly similar to that of CP-bound V-1 (Cα r.m.s.d.s of <0.50 A), indicating that CP does not induce a large conformational change in V-1. Detailed structural comparisons using the computational program All Atom Motion Tree revealed that CP binding can be accomplished by minor side-chain rearrangements of several residues. These findings are consistent with the known biological role of V-1, in which it globally inhibits CP in the cytoplasm.