PROSITE documentation PDOC52011

Peptidase family M2 domain profile

Members of the M2 family of peptidases, related to mammalian angiotensin converting enzyme (EC 3.4.15.1, ACE, peptidyl-dipeptidase A), play important roles in regulating a number of physiological processes. ACE is a membrane-bound, zinc dependent dipeptidase that catalyzes the conversion of the decapeptide angiotensin I to the potent vasopressor octapeptide angiotensin II by removing the two C-terminal amino acids. Bradykinin, a vasodilator, and the hemoregulatory peptide N-acetyl-Ser-Asp-Lys-Pro (AcSDKP) are also substrates for mammalian ACE. Two separate isoforms have been characterized: somatic (sACE) and testicular (germinal) ACE (tACE) are encoded by a single gene from two alternate promoters. The sACE polypeptide forms two homologous catalytically active extracellular domains, the N- and C-domains, each bearing an HExxH zinc-binding motif in the active site whereas the tACE isoform only forms a single domain that is essentially identical with the C-domain of sACE. The ACE homolog, ACE2 (EC 3.4.17.–), differs from ACE in being a carboxypeptidase that preferentially removes carboxy-terminal hydrophobic or basic amino acids; it appears to be important in cardiac function. Both ACE and ACE2 have catalytic activity that is chloride sensitive and is caused by the presence of the CL1 and CL2 chloride-binding sites in ACE and the CL1 site in ACE2. The chloride regulation of activity is also substrate dependent. It has been proposed that chloride binding induces subtle changes in the conformation of the active site, which either facilitate or hinder substrate binding. ACE homologs (also known as members of the M2 gluzincin family) have been found in a wide variety of species, even in those that neither have a cardiovascular system nor synthesize angiotensin. In vertebrates, the number of ACE genes appears to be limited to ACE and ACE2, but in some insects there has been a much greater expansion of this gene family. The function of these ACE-like proteins is largely unknown [1,2,3,4,5,6,7,8].

The overall structure of the M2 metallopeptidase domain is predominantly helical, consisting of twenty-one α-helices, nine 3(10) helices and two anti-parallel β-strands (see <PDB:5A2R>). The peptidase family M2 domain can be further divided into two subdomains (I and II), which form the two sides of a long and deep cleft. The two catalytic subdomains are connected only at the floor of the active site cleft. One prominent α-helix connects the two subdomains and forms part of the floor of the canyon. The zinc-binding site is located near the bottom and on one side of the large active site cleft (subdomain I side), nearly midway along its length. The zinc is coordinated by two His residues, one Glu, and one water molecule. These residues at the zinc-binding site make up the HEXXH+E motif conserved in the zinc metallopeptidase clan MA (see <PDOC00129>). Two chloride-binding sites are present in tACE. The N-domain of sACE possesses a CL2 site only, and so the enzyme has three chloride-binding sites in total. The CL2 chloride site is absent in ACE2. Consequently, ACE2 only binds a chloride ion at one CL1 site. The peptidase family M2 domain contains three conserved disulfide bonds, C1-C2, C3-C4, and C5-C6 [8,9,10,11,12].

The profile we developed covers the entire peptidase family M2 domain.