Kinetic and structural characterisation of domain-specific angiotensin I-converting enzyme inhibition by captopril, rentiapril and zofenoprilat

Angiotensin I-converting enzyme (ACE) is a zinc-dependent dipeptidyl carboxypeptidase involved in blood pressure regulation through proteolysis of angiotensin I (Ang-I) into the potent vasoconstrictor, angiotensin II (Ang-II). Inhibition of ACE is therefore used for the treatment of hypertension, heart failure, myocardial infarction, stroke and chronic kidney disease. Current ACE inhibitors (ACEi) bind both the N- and C-catalytic domains of ACE (referred to as nACE and cACE), and this has been linked to the occurrence of side effects due to the wide substrate specificity of ACE. The development of domain selective ACEi with reduced side effects is therefore key for improved therapeutic intervention. Understanding how current ACEi bind nACE and cACE, and their differences in domain selectivity should aid structure-based development of more selective ACEi by identifying different chemical groups that increase or decrease selectivity. We present the kinetic and structural characterisation of nACE and cACE with three thiolate ACEi, captopril (Ki, nACE = 2.53 nm and cACE = 2.04 nm), rentiapril (monomer Ki, nACE = 2.22 nm and cACE = 6.77 nm) and zofenoprilat (Ki, nACE = 2.86 nm and cACE = 0.61 nm). Detailed structural analysis indicated that the S2′ subsite likely contributes to the variation in domain selectivity observed for rentiapril and zofenoprilat due to differences in hydrophobicity and displacement of water molecules that contribute to ACE's hydration shell. Interestingly, in the cACE crystal structure, rentiapril bound as a dimer, and kinetic data revealed that both the monomeric and dimeric (dimer Ki, nACE = 15.11 nm and cACE = 36.38 nm) forms of rentiapril inhibit ACE with nanomolar affinity.