Structural studies on human Angiotensin-I converting enzyme (ACE) and the design of novel domain specific inhibitors

Angiotensin-I converting enzyme [ACE, which contains two domains (N and C)] inhibitors are widely used to treat cardiovascular diseases, including high blood pressure, heart failure, coronary artery disease, fibrosis and kidney failure. However, current-generation ACE inhibitors, which were developed in the 1970?s and 1980?s, are hampered by common side effects. While there are many ACE inhibitors on the market that block both domains, there are no drugs that selectively inhibit the N domain and thereby accrue the advantages of reducing fibrosis and inflammation in the heart, kidney and lung, without the concomitant side effects induced by blockade of the C domain.. This underscores the importance of the determination of the 3D structure of ACE and the design of 2nd generation ACE-inhibitor complex/s that are safer and more effective. Our success in the determination of the crystal structure of human testis ACE (equivalent to the C domain of somatic ACE) and the N-domain of somatic ACE using X-ray crystallography have provided the platform for true structure-based design of ACE inhibitors. This is a significant breakthrough in terms of the structural biology of the protease and, more importantly, the mechanism of ACE inhibition. This paves the way for a more rigorous approach exploiting the differences between the domains through a structure based drug design approach of novel domain-selective inhibitors. Our proposed experiments are directed at structural study of the full-length somatic ACE and crystal structures of complexes of ACE with domain selective inhibitors combining basic and translational research on a important medical problem.

Somatic angiotensin-I converting enzyme (ACE) - well known for its role in cardiovascular pathophysiology has an unusual, two-domain, double active-site structure. The two domains (designated N and C) are ~55% identical and each contains a similar active site with overlapping but distinct substrate preferences. While both convert angiotensin I to angiotensin II in vitro, current evidence suggests the C domain site predominates in this role in vivo. The N domain site inactivates a hemoregulatory and antifibrotic peptide, AcSDKP, in vivo. However, differences in the characteristics of the two domains may result in different context-dependent activities, as is the case with other enzymes containing tandem repeats. The N domain may also have a role in modulating C domain activity, through a combination of inter-domain cooperativity and structural stabilisation. Recent work on ACE active-site mutants containing one or more key residues replaced by their cognate residues from the other domain, synthesis of domain-selective inhibitors, and co-crystal structures of each domain with such inhibitors, has led to a better insight of the basis for domain selectivity and should enable the design of next-generation, domain-selective inhibitors with distinct pharmacological profiles. In addition, a recent report on the inactivation of the N-terminal catalytic site of ACE significantly reduces bleomycin-induced lung fibrosis and implicates AcSDKP in the mechanism of protection. This work makes a compelling case for the use of N-selective ACE inhibitors for increasing tolerance to bleomycin in cancer therapy and treatment of fibrosing lung diseases. In parallel, the proposed research would also help in better understanding the relationship between the structure and function of somatic ACE.