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Leukotriene (LT) A4 hydrolase/aminopeptidase is a bifunctional zinc enzyme that
catalyzes the final step in the biosynthesis of LTB4, a potent chemoattractant
and immune modulating lipid mediator. Here, we report a high-resolution crystal
structure of LTA4 hydrolase in complex with captopril, a classical inhibitor of
the zinc peptidase angiotensin-converting enzyme. Captopril makes few
interactions with the protein, but its free thiol group is bound to the zinc,
apparently accounting for most of its inhibitory action on LTA4 hydrolase. In
addition, we have determined the structures of LTA4 hydrolase in complex with
two selective tight-binding inhibitors, a thioamine and a hydroxamic acid. Their
common benzyloxyphenyl tail, designed to mimic the carbon backbone of LTA4,
binds into a narrow hydrophobic cavity in the protein. The free hydroxyl group
of the hydroxamic acid makes a suboptimal, monodentate complex with the zinc,
and strategies for improved inhibitor design can be deduced from the structure.
Taken together, the three crystal structures provide the molecular basis for the
divergent pharmacological profiles of LTA4 hydrolase inhibitors. Moreover, they
help define the binding pocket for the fatty acid-derived epoxide LTA4 as well
as the subsites for a tripeptide substrate, which in turn have important
implications for the molecular mechanisms of enzyme catalyses.
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