Cryo‐EM reveals mechanisms of angiotensin I‐converting enzyme allostery and dimerization

Abstract

Hypertension (high blood pressure) is a major risk factor for cardiovascular disease, which is the leading cause of death worldwide. The somatic isoform of angiotensin I‐converting enzyme (sACE) plays a critical role in blood pressure regulation, and ACE inhibitors are thus widely used to treat hypertension and cardiovascular disease. Our current understanding of sACE structure, dynamics, function, and inhibition has been limited because truncated, minimally glycosylated forms of sACE are typically used for X‐ray crystallography and molecular dynamics simulations. Here, we report the first cryo‐EM structures of full‐length, glycosylated, soluble sACE (sACE S1211 ). Both monomeric and dimeric forms of the highly flexible apo enzyme were reconstructed from a single dataset. The N‐ and C‐terminal domains of monomeric sACE S1211 were resolved at 3.7 and 4.1 Å, respectively, while the interacting N‐terminal domains responsible for dimer formation were resolved at 3.8 Å. Mechanisms are proposed for intradomain hinging, cooperativity, and homodimerization. Furthermore, the observation that both domains were in the open conformation has implications for the design of sACE modulators. image Angiotensin I‐converting enzyme (sACE) is crucial for blood pressure regulation and is thus an important drug target, yet its structure and mechanisms of hinge motions and dimerization are poorly understood. Here, cryo‐EM reveals structures of the highly dynamic monomeric and dimeric sACE. The active sites of the sACE two‐domain protein are in an open conformation for both monomeric and dimeric forms but undergo continuous breathing to transition towards a closed state. sACE is highly dynamic with bending, pivoting, and jumping domain motions about the interdomain linker. Allosteric site predictions provide insight into intra‐ and interdomain cooperativity. Dimerization near an allosteric site increases linker dynamics and causes rotameric changes in key N‐domain active site residues.