# Molecular basis of domain‐specific angiotensin I‐converting enzyme inhibition by the antihypertensive drugs enalaprilat, ramiprilat, trandolaprilat, quinaprilat and perindoprilat

## TL;DR

This study examines how five ACE inhibitors interact with different parts of the ACE enzyme to cause side effects and suggests ways to design better drugs.

## Contribution

The study provides new structural and kinetic insights into domain-specific inhibition of ACE by clinically used inhibitors.

## Key findings

- Trandolaprilat has the highest affinity for both nACE and cACE domains.
- Quinaprilat shows the greatest cACE selectivity among the inhibitors.
- Inhibitors do not use unique residues in nACE/cACE for domain selectivity.

## Abstract

Angiotensin I‐converting enzyme (ACE) is a dipeptidyl carboxypeptidase with two homologous catalytic domains [N‐ and C‐domains (nACE and cACE)] that can cleave a range of substrates. cACE primarily cleaves the inactive decapeptide angiotensin I into the potent vasopressor angiotensin II, whereas nACE preferentially cleaves the antifibrotic tetrapeptide N‐acetyl‐seryl‐aspartyl‐lysyl‐proline (Ac‐SDKP). Several ACE inhibitors, which bind to both cACE and nACE active sites, are used clinically for the treatment of hypertension; however, serious side effects are seen in ~ 20–25% of patients due to nonselective inhibition. To improve ACE inhibitor side effect profiles, the design and development of selective inhibitors of cACE or nACE is desirable for the treatment of hypertension or fibrosis. The detailed molecular basis through which the clinically available ACE inhibitors bind and inhibit cACE and nACE was unknown. Thus, in this study, we have characterised the structural and kinetic basis for the interaction between cACE and nACE with enalaprilat, ramiprilat, trandolaprilat, quinaprilat and perindoprilat. The inhibitors display nanomolar inhibition of both domains, with moderate‐to‐low cACE‐selectivity. Trandolaprilat possesses the highest affinity for both nACE and cACE, whereas quinaprilat displayed the largest cACE‐selectivity. None of the binding modes of the inhibitors extend beyond the S1–S2′ subsites to make use of the unique nACE/cACE residues that have been shown to influence domain selectivity. These findings supplement our understanding of ACE inhibition by the clinically used ACE inhibitors, and this information should be useful in the future design of more domain‐selective inhibitors for the treatment of hypertension and cardiovascular diseases.

Inhibition of angiotensin I‐converting enzyme is an effective strategy for the treatment of hypertension. However, the clinically available ACE inhibitors cause side effects due to nonselective inhibition of the two catalytic domains of ACE (nACE and cACE). Here, we present the kinetic and structural characterisation of nACE and cACE with the ACE inhibitors enalaprilat, ramiprilat, trandolaprilat, quinaprilat and perindoprilat to supplement our understanding of domain selectivity. Figure was produced using ccp4mg.