The Angiotensin-converting Enzyme 2 (ACE2) Family
ACE2 is a receptor for the COVID-19-causing virus, CoV-2. It is cleaved by transmembrane proteases during host cell infection, thus reducing its activities. ACE2 is a relevant player in the renin-angiotensin system (RAS), counterbalancing the deleterious effects of angiotensin II. Intestinal ACE2 functions as a chaperone for the amino acid transporter B(0)AT1 (TC# 2.A.22.6.3). ACE2 may serve as a chaperone protein, stabilizing the neutral amino acid transporter, B(0)AT1 (Sharma et al. 2020). ACE2-mediated dysregulation of SGLT1 in the intestinal epithelium links it to the pathogenesis of diabetes mellitus which can be a reason for the associated mortality in COVID-19 patients with diabetes (Kumar et al. 2020). The major route of entry for SARS-CoV-2 into human cells is by means of the ACE2) receptor. This zinc-containing carboxypeptidase and membrane-integral surface receptor is ubiquitous and widely expressed in multiple cell types (Zhao et al. 2021). PDZ-containing proteins are targeted by the ACE2 receptor (Caillet-Saguy and Wolff 2021).
Possibly, the B(0)AT1/ACE2 complex in the intestinal epithelium regulates the gut microbiota (GM) composition and function, with important repercussions on local and systemic immune responses against pathogenic agents such as viruses. Productive infection of SARS-CoV-2 in ACE2+ mature human enterocytes and patients' GM dysbiosis has been demonstrated. Viana et al. 2020 outlined the evidence linking abnormal ACE2 functions with the poor outcomes (higher disease severity and mortality rate) in COVID-19 patients with pre-existing age-related co-morbidities and addresses a possible role for GM dysbiosis. There are therapeutic possibilities based on these pathways (Viana et al. 2020). Atrial and ventricular cardiomyocytes have increased levels of ACE2 and other proteins that facilitate viral entry, and are therefore susceptible to SARS-CoV-2 infection (Yang et al. 2021).
ACE2 is a transmembrane protein and as a soluble catalytic ectodomain of ACE2, also known as the soluble ACE2 that can be found in plasma and other body fluids. ACE2 regulates the local actions of the renin-angiotensin system in cardiovascular tissues, and the ACE2/Angiotensin 1-7 axis exerts protective actions in cardiovascular disease (García-Escobar et al. 2021). Increasing soluble ACE2 is associated with heart failure, cardiovascular disease, and cardiac remodelling. García-Escobar et al. 2021 reviewed of the molecular structure and biochemical functions of ACE2, and updated the evidence, clinical applications, and emerging potential therapies with the ACE2 in heart failure, cardiovascular disease, lung injury, and COVID-19 infection. Antihypertensive activities of two ACE-renin inhibitory peptides has been reported (Ma et al. 2021).
ACE2 of 805 aas and 2 TMSs, one N-terminal and one C-terminal, the latter anchoring the protein in the membrane. It is a chaparone protein for the B0AT1 amino acid transporter (TC# 2.A.22.6.3) (see family description).
ACE2 of Homo sapiens
Angiotensin-converting enzyme, ACE, of 724 aas and 2 or possibly 3 TMSs. One is at the N-terminus of the protein, one is at the C-terminus, and one is near the middle of the protein.
ACE2 of Apis cerana
M2 family metallopeptidase of 562 aas and one N-terminal TMS.
Peptidase of Lentimicrobium saccharophilum
Peptidyl-dipeptidase A of 529 aa
Peptidase of Melghirimyces algeriensis