1AM5

There are many different proteins and EC numbers represented by the aspartic endopeptidase family. They are highly conserved and digestive proteases present in vertebrates, fungi, plants, retroviruses, and plant viruses. The catalytic site of pepsin-like enzymes is formed at the junction of the two domains of the protein and contains two catalytic aspartic acid residues, one in each domain. Although they vary widely in their substrate specificity, they all hydrolyse perform the hydrolysis of a peptide chain using a asparate catalytic duo which are found in a neutral and negatively charged state. Aspartate endopeptidases represented here include:

• Pepsin A, EC:3.4.23.1, shows particularly broad specificity; although bonds involving phenylalanine and leucine are preferred, many others are also cleaved to some extent. Preferential cleavage: hydrophobic, preferably aromatic, residues in P1 and P1' positions. Cleaves 1-Phe-|-Val-2, 4-Gln-|-His-5, 13-Glu-|-Ala-14, 14-Ala-|-Leu-15, 15-Leu-|-Tyr-16, 16-Tyr-|-Leu-17, 23-Gl90-y-|-Phe-24, 24-Phe-|-Phe-25 and 25-Phe-|-Tyr-26 bonds in the B chain of insulin.
• Gastricsin, EC:3.4.23.3, which shows a more restricted specificity than pepsin A, but shows preferential cleavage at Tyr-|-Xaa bonds. High activity on hemoglobin.
• Chymosin, EC:3.4.23.4, which is synthesized in the mucosa of the abomasum (fourth stomach) of young (unweaned) ruminants. The enzyme hydrolyzes casein to paracasein. It has broad specificity similar to that of pepsin A. Clots milk by cleavage of a single 104-Ser-Phe-|-Met-Ala-107 bond in kappa-chain of casein. It has historically been use in cheese manufacturing as a milk clotting initiator.
• Cathepsin D, EC:3.4.23.5, is post-translationally cleaved into two chains (the light and heavy chains). It is active in intracellular protein breakdown. Plays a role in APP processing following cleavage and activation by ADAM30 which leads to APP degradation (PubMed:27333034). Involved in the pathogenesis of several diseases such as breast cancer and possibly Alzheimer disease and has a specificity similar to, but narrower than, that of pepsin A. Does not cleave the 4-Gln-|-His-5 bond in B chain of insulin.
• Renin, EC:3.4.23.15, which is known to be a highly specific endopeptidase, whose only known function is to generate angiotensin I from angiotensinogen in the plasma, initiating a cascade of reactions that produce an elevation of blood pressure and increased sodium retention by the kidney.
• Penicillopepsin, EC:3.4.23.20, which catalyses the hydrolysis of proteins with broad specificity similar to that of pepsin A, preferring hydrophobic residues at P1 and P1', but also cleaving 20-Gly-|-Glu-21 in the B chain of insulin. Clots milk, and activates trypsinogen.
• Rhizopuspepsin, EC:3.4.23.21, which catalyses the hydrolysis of proteins with broad specificity similar to that of pepsin A, preferring hydrophobic residues at P1 and P1'. Clots milk and activates trypsinogen. Does not cleave 4-Gln-|-His-5, but does cleave 10-His-|-Leu-11 and 12-Val-|-Glu-13 in B chain of insulin.
• Endothiapepsin, EC:3.4.23.22, which catalyses the hydrolysis of proteins with specificity similar to that of pepsin A, prefers hydrophobic residues at P1 and P1', but does not cleave 14-Ala-|-Leu-15 in the B chain of insulin or Z-Glu-Tyr. Clots milk. Investigation into the inhibition of endothiapepsin has been aimed at forming an inhibitor for renin, another aspartic protease responsible for the formation of the potentially vasoactive peptide angiotensin II.
• Mucorpepsin, EC:3.4.23.23, which catalyses the hydrolysis of proteins, favoring hydrophobic residues at P1 and P1'. Clots milk. Does not accept Lys at P1, and hence does not activate trypsinogen.
• Candidapepsin (SAP), EC:3.4.23.24, which acts as a virulence factor within fungal pathogen associated infections. Evidence suggests SAP can degrade proteins associated with immunological and structural defence roles, such and IgG heavy chains, keratin, acidified collagen and extracellular matrix proteins. Its inhibition plays a key role in fighting fungal deceases. It shows preferential cleavage at the carboxyl of hydrophobic amino acids, but fails to cleave 15-Leu-|-Tyr-16, 16-Tyr-|-Leu-17 and 24-Phe-|-Phe-25 of insulin B chain. Activates trypsinogen.
• Saccharopepsin, EC:3.4.23.25, implicated in the post-translational regulation of S.cerevisiae vacuolar proteinases. Acts on YSCB, on YSCY and on itself. Catalysis the hydrolysis of proteins with broad specificity for peptide bonds. Cleaves -Leu-Leu-|-Val-Tyr- bond in a synthetic substrate. Does not act on esters of Tyr or Arg.
• Plasmepsin-2, EC:3.4.23.39, which catalyses the hydrolysis of the bonds linking certain hydrophobic residues in hemoglobin or globin. Also cleaves small molecules substrates such as Ala-Leu-Glu-Arg-Thr-Phe-|-Phe(NO2)-Ser-Phe-Pro-Thr.