Advances in the structural basis for angiotensin-1 converting enzyme (ACE) inhibitors

Abstract

Human somatic angiotensin-converting enzyme (ACE) is a key zinc metallopeptidase that plays a pivotal role in the renin-angiotensin-aldosterone system (RAAS) by regulating blood pressure and electrolyte balance. Inhibition of ACE is a cornerstone in the management of hypertension, cardiovascular diseases, and renal disorders. Recent advances in structural biology techniques have provided invaluable insights into the molecular mechanisms underlying ACE inhibition, facilitating the design and development of more effective therapeutic agents. This review focuses on the latest advancements in elucidating the structural basis for ACE inhibition. High-resolution crystallographic studies of minimally glycosylated individual domains of ACE have revealed intricate molecular details of the ACE catalytic N- and C-domains, and their detailed interactions with clinically relevant and newly designed domain-specific inhibitors. In addition, the recently elucidated structure of the glycosylated form of full-length ACE by cryo-electron microscopy (cryo-EM) has shed light on the mechanism of ACE dimerization and revealed continuous conformational changes which occur prior to ligand binding. In addition to these experimental techniques, computational approaches have also played a pivotal role in elucidating the structural basis for ACE inhibition. Molecular dynamics simulations and computational docking studies have provided atomic details of inhibitor binding kinetics and energetics, facilitating the rational design of novel ACE inhibitors with improved potency and selectivity. Furthermore, computational analysis of the motions observed by cryo-EM allowed the identification of allosteric binding sites on ACE. This affords new opportunities for the development of next-generation allosteric inhibitors with enhanced pharmacological properties. Overall, the insights highlighted in this review could enable the rational design of novel ACE inhibitors with improved efficacy and safety profiles, ultimately leading to better therapeutic outcomes for patients with hypertension and cardiovascular diseases.

Keywords: enzymology; inhibitor design; structural biology.

Figure 1. An overview of the renin–angiotensin–aldosterone system (RAAS)

A complex pathway of peptides converted to active hormones (orange rectangles) by peptidases (blue ovals) and key receptors (pink cylinders) provide a number of targets for therapeutic intervention. ACE, angiotensin-1 converting enzyme; ACE2, angiotensin-converting enzyme 2; AT₁R, angiotensin type 1 receptor: AT₂R, angiotensin type 2 receptor; MasR, Mas receptor for Ang-(1-7); ENP, endopeptidases. The effect of AT₁R, AT₂R, and MasR stimulation are shown under each receptor.

Figure 2. Schematic representation of the domain structure of sACE and tACE

LR linker region, NT N-terminus, SR stalk region, TM transmembrane region, CT C-terminus, HExxH zinc binding histidine and catalytic glutamate conserved motif. Glycosylation is shown by the black (always glycosylated), grey (partially glycosylated) and white (not glycosylated) circles.

Figure 3. Closed structures of nACE (PDB code: 2C6N, Corradi et al., 2006) and cACE (PDB code: 1O86, Natesh et al., 2003) in complex with lisinopril

Schematic representation of the overall structures of (A) nACE and (B) cACE inhibitor complexes (loop regions are shortened for clarity), with close-up view of bound lisinopril in the active site of (C) nACE and (D) cACE. Zinc ions and water molecules are depicted as grey and cyan spheres, respectively, with nACE and cACE helices coloured in orange and green, respectively. β-strands are coloured blue. Lisinopril and loop regions are coloured silver and pink for nACE and silver and purple for cACE.

Figure 4. Current clinically used ACE inhibitors

The chemical structures of 17 ACE inhibitors classified according to their zinc binding groups.

Figure 5. Structures of selective ACE inhibitors with K_i values for N-domain ACE (nACE) and C-domain ACE (cACE)

Figure 6. Structures of nACE (A), cACE (B), and NEP (C) in complex with the vasopeptidase inhibitor, omapatrilat

The structures of nACE, cACE and NEP are shown in orange, light green, and light blue respectively. Omapatrilat in nACE, cACE, and NEP is shown in magenta, purple, and pink, respectively.

Figure 7. Crystal structures of ‘closed’ and ‘open’ nACE

Sub-domain 1 is shown in yellow (The lid-like region in orange), and sub-domain 2 in green. The zinc ion is shown by the grey sphere.

Figure 8. Cryo -EM structures of open sACE (A) and nACE homodimer (B)

The α-helices of nACE and cACE are shown in orange and light green, respectively, and the linker region in black. The second molecule of the nACE homodimer is shown in red. β-strands are shown in blue. Glycosylated carbohydrates shown in yellow. The homodimer interface is shown in the dotted square. Dotted lines represent hydrogen bonding interactions, and the double arrow indicates π-stacking.