A Human Homolog of Angiotensin-converting Enzyme

Abstract

A novel human zinc metalloprotease that has considerable homology to human angiotensin-converting enzyme (ACE) (40% identity and 61% similarity) has been identified. This metalloprotease (angiotensin-converting enzyme homolog (ACEH)) contains a single HEXXH zinc-binding domain and conserves other critical residues typical of the ACE family. The predicted protein sequence consists of 805 amino acids, including a potential 17-amino acid N-terminal signal peptide sequence and a putative C-terminal membrane anchor. Expression in Chinese hamster ovary cells of a soluble, truncated form of ACEH, lacking the transmembrane and cytosolic domains, produces a glycoprotein of 120 kDa, which is able to cleave angiotensin I and angiotensin II but not bradykinin or Hip-His-Leu. In the hydrolysis of the angiotensins, ACEH functions exclusively as a carboxypeptidase. ACEH activity is inhibited by EDTA but not by classical ACE inhibitors such as captopril, lisinopril, or enalaprilat. Identification of the genomic sequence of ACEH has shown that the ACEH gene contains 18 exons, of which several have considerable size similarity with the first 17 exons of human ACE. The gene maps to chromosomal location Xp22. Northern blotting analysis has shown that the ACEH mRNA transcript is ϳ3.4 kilobase pairs and is most highly expressed in testis, kidney, and heart. This is the first report of a mammalian homolog of ACE and has implications for our understanding of cardiovascular and renal function.

A previously unknown reovirus of bat origin is associated with an acute respiratory disease in humans

“…Ephrin B2 has been identified as the main receptor for henipaviruses (30,31), and its wide distribution and status as a member of a conserved family of cell-surface glycoprotein ligands (32) may help to account for the wide host range of henipaviruses in vivo and in vitro. Similarly, the receptor for the SARS coronavirus, angiotensin-converting enzyme 2 (33), is also conserved among different animals (34), an observation consistent with the finding that SARS coronavirus seems to be able to infect most mammalian species tested under experimental conditions (35). In this regard, it is worth noting that MelV and PulV are also capable of replicating in a wide range of cell lines, including one derived from mosquitoes (see SI Table 2).…”

Angiotensin converting enzyme 2 (ACE2) activity in fetal calf serum: implications for cell culture research

“…In contrast, heat treatment for 30 min at 70°C completely abolished ACE2 activity in FCS. It is noteworthy that these findings are in keeping with the knowledge that the N-domain of somatic ACE, which is denatured at 70.5°C as compared to its C-domain with melting temperature of 55.3°C (Voronov et al 2002) more closely resembles ACE2 with *60% sequence similarity (Tipnis et al 2000). Although heat treatment to 70°C eliminated ACE2 activity it is unknown whether FCS treated in this way effects cell culture.…”

Hydrolysis of Biological Peptides by Human Angiotensin-converting Enzyme-related Carboxypeptidase

“…The molecular mass of the purified ACE2 (89.6 kDa, as determined by MALDI-TOF mass spectrometry) is greater than that predicted from the peptide sequence (85.314 kDa). The higher molecular mass is likely to be due to glycosylation, as has been reported for ACE2 (6). The ACE2 sample efficiently hydrolyzes the fluorogenic peptide Mca-APK(Dnp), with kinetic constants of K m ϭ 147 Ϯ 0.7 M, k cat ϭ 114 Ϯ 0.7 s Ϫ1 , and k cat /K m ϭ 7.7 ϫ 10 5 M Ϫ1 s Ϫ1 (n ϭ 2), as determined by an HPLC/UV detection-based assay, as described under "Experimental Procedures."…”

“…Similarly, Tipnis et al (6) reported that unpurified ACE2 expressed in Chinese hamster ovary cells catalyzes the hydrolysis of the C-terminal residue of Ang I and Ang II. Herein is the first report of characterization of the catalytic activity of purified ACE2.…”

“…ACE2 was identified as a zinc metalloprotease due to its canonical HEXXH sequence (amino acids 374 -378) (1), its inhibition by EDTA (6), and its sequence identity with the catalytic residues of ACE (7). The ACE inhibitors captopril, lisinopril, and enalaprilat are not inhibitors of ACE2 (1,6). The physiological and pathophysiological role of ACE2 is not yet clearly understood.…”