Conformational change in the vinculin C-terminal depends on a critical histidine residue (His-906)

A phospholipid-controlled interaction between the N-terminal and C-terminal domains of vinculin is thought to be a major mechanism that regulates bind ing activities of the protein. To probe the mechanisms underlying these int eractions we used chemical modification and site-directed mutagenesis direc ted at histidine residues. Diethylpyrocarbonate (DEPC) modification of the C-terminal, but not the N-terminal, domain greatly decreased affinity of th e N-terminal-C-terminal binding, implicating histidine residues in the C-te rminal. Mutation of either or both C-terminal histidines (at positions 906 and 1026), however, did not affect N-C binding at neutral pH. The H906A mut ation did prevent DEPC effects and also prevented the normal decrease in bi nding affinity for the N-terminal at lower pH. We found that the wild type C-terminal domain, but not the H906A mutant, underwent a conformational cha nge at pH 6.5, reflected in an altered circular dichroism spectrum and appa rent oligomerization. Phospholipid also induced conformational changes in t he wild type C-terminal domain but not in the H906A mutant, even though the mutant protein did bind to the phospholipid. Finally, the sensitivity of t he N-C interaction to phospholipid was much reduced by the H906A mutation. These results show that H906 plays a key role in the conformational dynamic s of the C-terminal domain and thus the regulation of vinculin.