Angiotensin-I converting enzyme (ACE, a zinc dependent dipeptidyl carboxypeptidase) is a major target of drugs due to its role in the modulation of blood pressure and cardiovascular disorders. Here we present a crystal structure of AnCE (an ACE homologue from Drosophila melanogaster with a single enzymatic domain) in complex with a natural product-phosphonotripeptide. K-26 at 1.96 angstrom resolution. The inhibitor binds exclusively in the S-1 and S-2 binding pockets of AnCE (coordinating the zinc ion) through ionic and hydrogen bond interactions. A detailed structural comparison of AnCE-K-26 complex with individual domains of human somatic ACE provides useful information for further exploration of ACE inhibitor pharmacophores involving phosphonic acids. (C) 2010 Elsevier Inc. All rights reserved.