Modulating the substrate specificity of LTA4H aminopeptidase by using chemical compounds and small-molecule-guided mutagenesis.

Leukotriene A(4) hydrolase (LTA4H) is a bifunctional zinc-containing enzyme with an epoxide hydrolase activity and an aminopeptidase activity of unclear function. The two activities occupy different, but overlapping sites. In this study we have focused on the non-overlapping regions of these sites and have found that a series of previously reported compounds-diphenyl ether, 4-phenoxyphenol, and their derivatives-can change the substrate specificity of LTA4H aminopeptidase, from arginyl peptide to alanyl peptide. The possible substrate specificity alteration mechanism was studied with the aid of molecular modeling and site-directed mutagenesis. Furthermore, several mutants that show different substrate specificity, such as F314E and V367W, were successfully designed by using the proposed small-molecule binding site as a model. F314E behaves as a highly selective aminopeptidase towards arginyl peptides with a selectivity increase of 850-fold, whereas V367W prefers alanyl peptides over arginyl peptides, just as the organic modulators do.