The influence of angiotensin converting enzyme mutations on the kinetics and dynamics of N-domain selective inhibition

ACE Phenotyping in Human Blood and Tissues: Revelation of ACE Outliers and Sex Differences in ACE Sialylation

Angiotensin-converting enzyme (ACE) metabolizes a number of important peptides participating in blood pressure regulation and vascular remodeling. Elevated ACE expression in tissues (which is generally reflected by blood ACE levels) is associated with an increased risk of cardiovascular diseases. Elevated blood ACE is also a marker for granulomatous diseases. Decreased blood ACE activity is becoming a new risk factor for Alzheimer's disease. We applied our novel approach-ACE phenotyping-to characterize pairs of tissues (lung, heart, lymph nodes) and serum ACE in 50 patients. ACE phenotyping includes (1) measurement of ACE activity with two substrates (ZPHL and HHL); (2) calculation of the ratio of hydrolysis of these substrates (ZPHL/HHL ratio); (3) determination of ACE immunoreactive protein levels using mAbs to ACE; and (4) ACE conformation with a set of mAbs to ACE. The ACE phenotyping approach in screening format with special attention to outliers, combined with analysis of sequencing data, allowed us to identify patient with a unique ACE phenotype related to decreased ability of inhibition of ACE activity by albumin, likely due to competition with high CCL18 in this patient for binding to ACE. We also confirmed recently discovered gender differences in sialylation of some glycosylation sites of ACE. ACE phenotyping is a promising new approach for the identification of ACE phenotype outliers with potential clinical significance, making it useful for screening in a personalized medicine approach.

Structural insights into the inhibitory mechanism of angiotensin-I-converting enzyme by the lactotripeptides IPP and VPP

Human somatic angiotensin-1-converting enzyme (sACE) is composed of a catalytic N-(nACE) and C-domain (cACE) of similar size with different substrate specificities. It is involved in the regulation of blood pressure by converting angiotensin I to the vasoconstrictor angiotensin II and has been a major focus in the development of therapeutics for hypertension. Bioactive peptides from various sources, including milk, have been identified as natural ACE inhibitors. We report the structural basis for the role of two lacototripeptides, Val-Pro-Pro and Ile-Pro-Pro, in domain-specific inhibition of ACE using X-ray crystallography and kinetic analysis. The lactotripeptides have preference for nACE due to altered polar interactions distal to the catalytic zinc ion. Elucidating the mechanism of binding and domain selectivity of these peptides also provides important insights into the functional roles of ACE.

Detection of Various Traditional Chinese Medicinal Metabolites as Angiotensin-Converting Enzyme Inhibitors: Molecular Docking, Activity Testing, and Surface Plasmon Resonance Approaches

Angiotensin-converting enzyme 1 (ACE1) is a peptide involved in fluid and blood pressure management. It regulates blood pressure by converting angiotensin I to angiotensin II, which has vasoconstrictive effects. Previous studies have shown that certain compounds of natural origin can inhibit the activity of angiotensin-converting enzymes and exert blood pressure-regulating effects. Surface Plasmon Resonance (SPR) biosensor technology is the industry standard method for observing biomolecule interactions. In our study, we used molecular simulation methods to investigate the docking energies of various herbal metabolites with ACE1 proteins, tested the real-time binding affinities between various herbal metabolites and sACE1 by SPR, and analyzed the relationship between real-time binding affinity and docking energy. In addition, to further explore the connection between inhibitor activity and real-time binding affinity, several herbal metabolites' in vitro inhibitory activities were tested using an ACE1 activity test kit. The molecular docking simulation technique's results and the real-time affinity tested by the SPR technique were found to be negatively correlated, and the virtual docking technique still has some drawbacks as a tool for forecasting proteins' affinities to the metabolites of Chinese herbal metabolites. There may be a positive correlation between the enzyme inhibitory activity and the real-time affinity detected by the SPR technique, and the results from the SPR technique may provide convincing evidence to prove the interaction between herbal metabolites and ACE1 target proteins.

Phosphinic Peptides as Tool Compounds for the Study of Pharmacologically Relevant Zn-Metalloproteases

Phosphinic peptides constitute an important class of bioactive compounds that have found a wide range of applications in the field of biology and pharmacology of Zn-metalloproteases, the largest family of proteases in humans. They are designed to mimic the structure of natural substrates during their proteolysis, thus acting as mechanism-based, transition state analogue inhibitors. A combination of electrostatic interactions between the phosphinic acid group and the Zn cation as well as optimal noncovalent enzyme-ligand interactions can result in both high binding affinity for the desired target and selectivity against other proteases. Due to these unique properties, phosphinic peptides have been mainly employed as tool compounds for (a) the purposes of rational drug design by serving as ligands in X-ray crystal structures of target enzymes and allowing the identification of crucial interactions that govern optimal molecular recognition, and (b) the delineation of biological pathways where Zn-metalloproteases are key regulators. For the latter objective, inhibitors of the phosphinopeptidic type have been used either unmodified or after being transformed to probes of various types, thus expanding the arsenal of functional tools available to researchers. The aim of this review is to summarize all recent research achievements in which phosphinic peptides have played a central role as tool compounds in the understanding of the mechanism and biological functions of Zn-metalloproteases in both health and disease.

Structural basis for the inhibition of human angiotensin-1 converting enzyme by fosinoprilat

Human angiotensin I-converting enzyme (ACE) has two isoforms, somatic ACE (sACE) and testis ACE (tACE). The functions of sACE are widespread, with its involvement in blood pressure regulation most extensively studied. sACE is composed of an N-domain (nACE) and a C-domain (cACE), both catalytically active but have significant structural differences, resulting in different substrate specificities. Even though ACE inhibitors are used clinically, they need much improvement because of serious side effects seen in patients (~ 25-30%) with long-term treatment due to nonselective inhibition of nACE and cACE. Investigation into the distinguishing structural features of each domain is therefore of vital importance for the development of domain-specific inhibitors with minimal side effects. Here, we report kinetic data and high-resolution crystal structures of both nACE (1.75 Å) and cACE (1.85 Å) in complex with fosinoprilat, a clinically used inhibitor. These structures allowed detailed analysis of the molecular features conferring domain selectivity by fosinoprilat. Particularly, altered hydrophobic interactions were observed to be a contributing factor. These experimental data contribute to improved understanding of the structural features that dictate ACE inhibitor domain selectivity, allowing further progress towards designing novel 2nd-generation domain-specific potent ACE inhibitors suitable for clinical administration, with a variety of potential future therapeutic benefits. DATABASE: The atomic coordinates and structure factors for nACE-fosinoprilat and cACE-fosinoprilat structures have been deposited with codes 7Z6Z and 7Z70, respectively, in the RCSB Protein Data Bank, www.pdb.org.

All-Atom Simulations of Human ACE2-Spike Protein RBD Complexes for SARS-CoV-2 and Some of its Variants: Nature of Interactions and Free Energy Diagrams for Dissociation of the Protein Complexes

The spike protein of SARS-CoV-2 is known to interact with the human ACE2 protein via its receptor binding domain (RBD). We have investigated the molecular nature of this interprotein interaction and the associated free energy diagrams for the unbinding of the two proteins for SARS-CoV-2 and some of its known variants through all-atom simulations. The present work involves generation and analysis of 2.5 μs of unbiased and 4.2 μs of biased molecular dynamics trajectories in total for five explicitly solvated RBD-ACE2 systems at full atomic level. First, we have made a comparative analysis of the details of residue-wise specific interactions of the spike protein with ACE2 for SARS-CoV-1 and SARS-CoV-2. It is found that the average numbers of both direct interprotein and water-bridged hydrogen bonds between the RBD and ACE2 are higher for SARS-CoV-2 than SARS-CoV-1. These higher hydrogen bonded interactions are further aided by enhanced nonspecific electrostatic attractions between the two protein surfaces for SARS-CoV-2. The free energy calculations reveal that there is an increase in the free energy barrier by ∼1.5 kcal/mol for the unbinding of RBD from ACE2 for SARS-CoV-2 compared to that for SARS-CoV-1. Subsequently, we considered the RBDs of three variants of SARS-CoV-2, namely N501Y, E484Q/L452R, and N440K. The free energy barrier of protein unbinding for the N501Y variant is found to be ∼4 kcal/mol higher than the wild type SARS-CoV-2 which can be attributed to additional specific interactions involving Tyr501 of RBD and Lys353 and Tyr42 of ACE2 and also enhanced nonspecific electrostatic interaction between the protein surfaces. For the other two mutant variants of E484Q/L452R and N440K, the free energy barrier for protein unbinding increases by ∼2 and ∼1 kcal/mol, respectively, compared with the wild type SARS-CoV-2, which can be attributed to an increase in the number of interprotein hydrogen bonds for the former and also to enhanced positive electrostatic potential on the RBD surfaces for both of the variants. The successive breaking of interprotein hydrogen bonds along the free energy pathway of the unbinding process is also found out for all five systems studied here.

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

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.

Probing the Requirements for Dual Angiotensin-Converting Enzyme C-Domain Selective/Neprilysin Inhibition

Selective inhibition of the angiotensin-converting enzyme C-domain (cACE) and neprilysin (NEP), leaving the ACE N-domain (nACE) free to degrade bradykinin and other peptides, has the potential to provide the potent antihypertensive and cardioprotective benefits observed for nonselective dual ACE/NEP inhibitors, such as omapatrilat, without the increased risk of adverse effects. We have synthesized three 1-carboxy-3-phenylpropyl dipeptide inhibitors with nanomolar potency based on the previously reported C-domain selective ACE inhibitor lisinopril-tryptophan (LisW) to probe the structural requirements for potent dual cACE/NEP inhibition. Here we report the synthesis, enzyme kinetic data, and high-resolution crystal structures of these inhibitors bound to nACE and cACE, providing valuable insight into the factors driving potency and selectivity. Overall, these results highlight the importance of the interplay between the S₁' and S₂' subsites for ACE domain selectivity, providing guidance for future chemistry efforts toward the development of dual cACE/NEP inhibitors.

Epitope mapping of novel monoclonal antibodies to human angiotensin I-converting enzyme

Angiotensin I-converting enzyme (ACE, CD143) plays a crucial role in blood pressure regulation, vascular remodeling, and immunity. A wide spectrum of mAbs to different epitopes on the N and C domains of human ACE have been generated and used to study different aspects of ACE biology, including establishing a novel approach-conformational fingerprinting. Here we characterized a novel set of 14 mAbs, developed against human seminal fluid ACE. The epitopes for these novel mAbs were defined using recombinant ACE constructs with truncated N and C domains, species cross-reactivity, ACE mutagenesis, and competition with the previously mapped anti-ACE mAbs. Nine mAbs recognized regions on the N domain, and 5 mAbs-on the C domain of ACE. The epitopes for most of these novel mAbs partially overlap with epitopes mapped onto ACE by the previously generated mAbs, whereas mAb 8H1 recognized yet unmapped region on the C domain where three ACE mutations associated with Alzheimer's disease are localized and is a marker for ACE mutation T877M. mAb 2H4 could be considered as a specific marker for ACE in dendritic cells. This novel set of mAbs can identify even subtle changes in human ACE conformation caused by tissue-specific glycosylation of ACE or mutations, and can detect human somatic and testicular ACE in biological fluids and tissues. Furthermore, the high reactivity of these novel mAbs provides an opportunity to study changes in the pattern of ACE expression or glycosylation in different tissues, cells, and diseases, such as sarcoidosis and Alzheimer's disease.

ACE2 and ACE: structure-based insights into mechanism, regulation and receptor recognition by SARS-CoV

Angiotensin converting enzyme (ACE) is well-known for its role in blood pressure regulation via the renin–angiotensin aldosterone system (RAAS) but also functions in fertility, immunity, haematopoiesis and diseases such as obesity, fibrosis and Alzheimer’s dementia. Like ACE, the human homologue ACE2 is also involved in blood pressure regulation and cleaves a range of substrates involved in different physiological processes. Importantly, it is the functional receptor for severe acute respiratory syndrome (SARS)-coronavirus (CoV)-2 responsible for the 2020, coronavirus infectious disease 2019 (COVID-19) pandemic. Understanding the interaction between SARS-CoV-2 and ACE2 is crucial for the design of therapies to combat this disease. This review provides a comparative analysis of methodologies and findings to describe how structural biology techniques like X-ray crystallography and cryo-electron microscopy have enabled remarkable discoveries into the structure–function relationship of ACE and ACE2. This, in turn, has enabled the development of ACE inhibitors for the treatment of cardiovascular disease and candidate therapies for the treatment of COVID-19. However, despite these advances the function of ACE homologues in non-human organisms is not yet fully understood. ACE homologues have been discovered in the tissues, body fluids and venom of species from diverse lineages and are known to have important functions in fertility, envenoming and insect–host defence mechanisms. We, therefore, further highlight the need for structural insight into insect and venom ACE homologues for the potential development of novel anti-venoms and insecticides.

Angiotensin-converting enzyme open for business: structural insights into the subdomain dynamics

Angiotensin‐1‐converting enzyme (ACE) is a key enzyme in the renin–angiotensin–aldosterone and kinin systems where it cleaves angiotensin I and bradykinin peptides, respectively. However, ACE also participates in numerous other physiological functions, can hydrolyse many peptide substrates and has various exo‐ and endopeptidase activities. ACE achieves this complexity by containing two homologous catalytic domains (N‐ and C‐domains), which exhibit different substrate specificities. Here, we present the first open conformation structures of ACE N‐domain and a unique closed C‐domain structure (2.0 Å) where the C terminus of a symmetry‐related molecule is observed inserted into the active‐site cavity and binding to the zinc ion. The open native N‐domain structure (1.85 Å) enables comparison with ACE2, a homologue previously observed in open and closed states. An open S₂_S′‐mutant N‐domain structure (2.80 Å) includes mutated residues in the S₂ and S′ subsites that effect ligand binding, but are distal to the binding site. Analysis of these structures provides important insights into how structural features of the ACE domains are able to accommodate the wide variety of substrates and allow different peptidase activities.

Database

The atomic coordinates and structure factors for Open nACE, Open S2_S′‐nACE and Native G13‐cACE structures have been deposited with codes 6ZPQ, 6ZPT and 6ZPU, respectively, in the RCSB Protein Data Bank, www.pdb.org

ACE-domain selectivity extends beyond direct interacting residues at the active site

Angiotensin-converting enzyme (ACE) is best known for its formation of the vasopressor angiotensin II that controls blood pressure but is also involved in other physiological functions through the hydrolysis of a variety of peptide substrates. The enzyme contains two catalytic domains (nACE and cACE) that have different affinities for ACE substrates and inhibitors. We investigated whether nACE inhibitor backbones contain a unique property which allows them to take advantage of the hinging of nACE. Kinetic analysis showed that mutation of unique nACE residues, in both the S2 pocket and around the prime subsites (S′) to their C-domain counterparts, each resulted in a decrease in the affinity of nACE specific inhibitors (SG6, 33RE and ketoACE-13) but it required the combined S2_S′ mutant to abrogate nACE-selectivity. However, this was not observed with the non-domain-selective inhibitors enalaprilat and omapatrilat. High-resolution structures were determined for the minimally glycosylated nACE with the combined S2_S′ mutations in complex with the ACE inhibitors 33RE (1.8 Å), omapatrilat (1.8 Å) and SG6 (1.7 Å). These confirmed that the affinities of the nACE-selective SG6, 33RE and ketoACE-13 are not only affected by direct interactions with the immediate environment of the binding site, but also by more distal residues. This study provides evidence for a more general mechanism of ACE inhibition involving synergistic effects of not only the S2, S1′ and S2′ subsites, but also residues involved in the sub-domain interface that effect the unique ways in which the two domains stabilize active site loops to favour inhibitor binding.

Crystal structures of angiotensin-converting enzyme from Anopheles gambiae in its native form and with a bound inhibitor

The mosquitoes of the Anopheles and Aedes genus are some of the most deadly insects to humans because of their effectiveness as vectors of malaria and a range of arboviruses, including yellow fever, dengue, chikungunya, West Nile and Zika. The use of insecticides from different chemical classes is a key component of the integrated strategy against An. gambiae and Ae. aegypti, but the problem of insecticide resistance means that new compounds with different modes of action are urgently needed to replace chemicals that fail to control resistant mosquito populations. We have previously shown that feeding inhibitors of peptidyl dipeptidase A to both An. gambiae and Ae. aegypti mosquito larvae lead to stunted growth and mortality. However, these compounds were designed to inhibit the mammalian form of the enzyme (angiotensin-converting enzyme, ACE) and hence can have lower potency and lack selectivity as inhibitors of the insect peptidase. Thus, for the development of inhibitors of practical value in killing mosquito larvae, it is important to design new compounds that are both potent and highly selective. Here, we report the first structures of AnoACE2 from An. gambiae in its native form and with a bound human ACE inhibitor fosinoprilat. A comparison of these structures with human ACE (sACE) and an insect ACE homologue from Drosophila melanogaster (AnCE) revealed that the AnoACE2 structure is more similar to AnCE. In addition, important elements that differ in these structures provide information that could potentially be utilised in the design of chemical leads for selective mosquitocide development.

Interacting cogs in the machinery of the renin angiotensin system

Somatic angiotensin converting enzyme (sACE) is well-known for its role in blood pressure regulation and consequently, ACE inhibitors are widely prescribed for the treatment of hypertension. More than 60 years after the discovery of sACE, however, the molecular details of its substrate hydrolysis and inhibition are still poorly understood. Isothermal titration calorimetry, molecular dynamics simulations and fine epitope mapping suggest that substrate or inhibitor binding triggers a hinging motion between the two subdomains of each domain. Ligand binding to one domain further induces a conformational change in sACE to negatively affect the second domain's function and can also cause dimerization between sACE molecules. This has been linked to an increase in sACE expression via intracellular signalling. Inhibitor-induced dimerization could thus decrease the efficacy of hypertension treatment. At present, the only structural information available for sACE are crystal structures of the truncated domains in the closed conformation due to the presence of ligands. These structures do not provide any information regarding the open active site conformation prior to ligand binding, the relative orientation of the two domains in full-length sACE, or the dimerization interface. To guarantee effective therapeutic intervention, further research is required to investigate the hinging, negative cooperativity and dimerization of sACE. This review describes our current understanding of these interactions and proposes how recent advances in cryo-electron microscopy could enable structural elucidation of their mechanisms.

Structural basis for the C-domain-selective angiotensin-converting enzyme inhibition by bradykinin-potentiating peptide b (BPPb)

Angiotensin-converting enzyme (ACE) is a zinc metalloprotease best known for its role in blood pressure regulation. ACE consists of two homologous catalytic domains, the N- and C-domain, that display distinct but overlapping catalytic functions in vivo owing to subtle differences in substrate specificity. While current generation ACE inhibitors target both ACE domains, domain-selective ACE inhibitors may be clinically advantageous, either reducing side effects or having utility in new indications. Here, we used site-directed mutagenesis, an ACE chimera and X-ray crystallography to unveil the molecular basis for C-domain-selective ACE inhibition by the bradykinin-potentiating peptide b (BPPb), naturally present in Brazilian pit viper venom. We present the BPPb N-domain structure in comparison with the previously reported BPPb C-domain structure and highlight key differences in peptide interactions with the S4 to S9 subsites. This suggests the involvement of these subsites in conferring C-domain-selective BPPb binding, in agreement with the mutagenesis results where unique residues governing differences in active site exposure, lid structure and dynamics between the two domains were the major drivers for C-domain-selective BPPb binding. Mere disruption of BPPb interactions with unique S2 and S4 subsite residues, which synergistically assist in BPPb binding, was insufficient to abolish C-domain selectivity. The combination of unique S9–S4 and S2′ subsite C-domain residues was required for the favourable entry, orientation and thus, selective binding of the peptide. This emphasizes the need to consider factors other than direct protein–inhibitor interactions to guide the design of domain-selective ACE inhibitors, especially in the case of larger peptides.

Advances in Structural Biology of ACE and Development of Domain Selective ACE-inhibitors

BACKGROUND

The Angiotensin-I converting enzyme (ACE) is one of the most important components of the renin-angiotensin-aldosterone system controlling blood pressure and renal functions. Inhibitors of ACE are first line therapeutics used in the treatment of hypertension and related cardiovascular diseases. Somatic ACE consists of two homologous catalytic domains, the C- and N-domains. Recent findings have shown that although both domains are highly homologous in structure, they may have different physiological functions. The C-domain is primarily involved in the control of blood pressure, in contrast to the N-domain that is engaged in the regulation of hematopoietic stem cell proliferation. The currently available ACE inhibitors have some adverse effects that can be attributed to the non-selective inhibition of both domains. In addition, specific Ndomain inhibitors have emerged as potential antifibrotic drugs. Therefore, ACE is still an important drug target for the development of novel domain-selective drugs not only for the cardiovascular system but also for other systems.

OBJECTIVE

Detailed structural information about interactions in the protein-ligand complex is crucial for rational drug design. This review highlights the structural information available from crystallographic data which is essential for the development of domain selective inhibitors of ACE.

METHODS

Over eighty crystal complexes of ACE are placed into the Protein Database. An overview of X-ray ACE complexes with various inhibitors in C- and N-domains and an analysis of their binding mode have given mechanistic explanation of the structural determinants of selective ligand binding. In addition, ACE domain selective inhibitors with dual modes of action in complexes with ACE are also discussed.

CONCLUSION

Selectivity of ACE inhibitors for the N- and C-domain is controlled by subtle differences in the amino-acids forming the active site. Reported studies of crystal complexes of inhibitors in the C- and N-domains revealed that most selective inhibitors interact with non-conserved amino-acids between domains and have distinct interactions with the residues in the S2 and S2' subsites of the ACE catalytic site. Moreover, unusual binding of the second molecule of inhibitors in the binding cavity opens new possibilities of exploiting more distant regions of the catalytic center in structure-based design of novel drugs.

Recent developments in the synthesis and applications of phosphinic peptide analogs

Synthetic pseudopeptides that fit well with the active site architecture allow the most effective binding to enzymes, similar to native substrates in high-energy transition states. Phosphinic acid peptide analogs that comprise the tetrahedral phosphorus moiety introduced to replace an internal amide bond exert such an isosteric or isoelectronic resemblance, combined with providing other advantageous features, for example, metal complexing properties. Accordingly, they are capable of inhibiting metal-dependent enzymes involved in biological functions in eukaryotic and prokaryotic cells. These enzymes are associated with notorious human diseases, such as cancer, e.g., matrix metalloproteinases, or are etiological factors of protozoal and bacterial infections, e.g., metalloaminopeptidases. The affinity and selectivity of these compounds can be conveniently adjusted, either by structural modification of dedicated side chains or by backbone elongation to enhance specific interactions with the corresponding binding pockets. Recent approaches to the synthesis of these compounds are illustrated by examples of the preparation of rationally designed structures of inhibitors of particular enzymes. Activity against appealing enzymatic targets is presented, along with the molecular mechanisms of action and therapeutic implications. Innovative aspects of phosphinic peptide application, e.g., as activity-based probes, and ligands of complexes of radioisotopes for nuclear medicine are also outlined.

Crystal structures of sampatrilat and sampatrilat-Asp in complex with human ACE - a molecular basis for domain selectivity

Angiotensin‐1‐converting enzyme (ACE) is a zinc metallopeptidase that consists of two homologous catalytic domains (known as nACE and cACE) with different substrate specificities. Based on kinetic studies it was previously reported that sampatrilat, a tight‐binding inhibitor of ACE, K_i = 13.8 nm and 171.9 nm for cACE and nACE respectively [Sharma et al., Journal of Chemical Information and Modeling (2016), 56, 2486–2494], was 12.4‐fold more selective for cACE. In addition, samAsp, in which an aspartate group replaces the sampatrilat lysine, was found to be a nonspecific and lower micromolar affinity inhibitor. Here, we report a detailed three‐dimensional structural analysis of sampatrilat and samAsp binding to ACE using high‐resolution crystal structures elucidated by X‐ray crystallography, which provides a molecular basis for differences in inhibitor affinity and selectivity for nACE and cACE. The structures show that the specificity of sampatrilat can be explained by increased hydrophobic interactions and a H‐bond from Glu403 of cACE with the lysine side chain of sampatrilat that are not observed in nACE. In addition, the structures clearly show a significantly greater number of hydrophilic and hydrophobic interactions with sampatrilat compared to samAsp in both cACE and nACE consistent with the difference in affinities. Our findings provide new experimental insights into ligand binding at the active site pockets that are important for the design of highly specific domain selective inhibitors of ACE.

Database

The atomic coordinates and structure factors for N‐ and C‐domains of ACE bound to sampatrilat and sampatrilat‐Asp complexes (6F9V, 6F9R, 6F9T and 6F9U respectively) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

The Design and Development of a Potent and Selective Novel Diprolyl Derivative That Binds to the N-Domain of Angiotensin-I Converting Enzyme

Angiotensin-I converting enzyme (ACE) is a zinc metalloprotease consisting of two catalytic domains (N- and C-). Most clinical ACE inhibitor(s) (ACEi) have been shown to inhibit both domains nonselectively, resulting in adverse effects such as cough and angioedema. Selectively inhibiting the individual domains is likely to reduce these effects and potentially treat fibrosis in addition to hypertension. ACEi from the GVK Biosciences database were inspected for possible N-domain selective binding patterns. From this set, a diprolyl chemical series was modeled using docking simulations. The series was expanded based on key target interactions involving residues known to impart N-domain selectivity. In total, seven diprolyl compounds were synthesized and tested for N-domain selective ACE inhibition. One compound with an aspartic acid in the P₂ position (compound 16) displayed potent inhibition (K_i = 11.45 nM) and was 84-fold more selective toward the N-domain. A high-resolution crystal structure of compound 16 in complex with the N-domain revealed the molecular basis for the observed selectivity.