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Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called proteases, but may also occur by intra-molecular digestion.
A protease is an enzyme that catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products. They do this by cleaving the peptide bonds within proteins by hydrolysis, a reaction where water breaks bonds. Proteases are involved in many biological functions, including digestion of ingested proteins, protein catabolism, and cell signaling.
In biology and biochemistry, protease inhibitors, or antiproteases, are molecules that inhibit the function of proteases. Many naturally occurring protease inhibitors are proteins.
Aspartate transaminase (AST) or aspartate aminotransferase, also known as AspAT/ASAT/AAT or (serum) glutamic oxaloacetic transaminase, is a pyridoxal phosphate (PLP)-dependent transaminase enzyme that was first described by Arthur Karmen and colleagues in 1954. AST catalyzes the reversible transfer of an α-amino group between aspartate and glutamate and, as such, is an important enzyme in amino acid metabolism. AST is found in the liver, heart, skeletal muscle, kidneys, brain, red blood cells and gall bladder. Serum AST level, serum ALT level, and their ratio are commonly measured clinically as biomarkers for liver health. The tests are part of blood panels.
A catalytic triad is a set of three coordinated amino acids that can be found in the active site of some enzymes. Catalytic triads are most commonly found in hydrolase and transferase enzymes. An acid-base-nucleophile triad is a common motif for generating a nucleophilic residue for covalent catalysis. The residues form a charge-relay network to polarise and activate the nucleophile, which attacks the substrate, forming a covalent intermediate which is then hydrolysed to release the product and regenerate free enzyme. The nucleophile is most commonly a serine or cysteine amino acid, but occasionally threonine or even selenocysteine. The 3D structure of the enzyme brings together the triad residues in a precise orientation, even though they may be far apart in the sequence.
Aspartic proteases are a catalytic type of protease enzymes that use an activated water molecule bound to one or more aspartate residues for catalysis of their peptide substrates. In general, they have two highly conserved aspartates in the active site and are optimally active at acidic pH. Nearly all known aspartyl proteases are inhibited by pepstatin.
TEV protease is a highly sequence-specific cysteine protease from Tobacco Etch Virus (TEV). It is a member of the PA clan of chymotrypsin-like proteases. Due to its high sequence specificity, TEV protease is frequently used for the controlled cleavage of fusion proteins in vitro and in vivo.
In molecular biology, Proteinase K is a broad-spectrum serine protease. The enzyme was discovered in 1974 in extracts of the fungus Parengyodontium album. Proteinase K is able to digest hair (keratin), hence, the name "Proteinase K". The predominant site of cleavage is the peptide bond adjacent to the carboxyl group of aliphatic and aromatic amino acids with blocked alpha amino groups. It is commonly used for its broad specificity. This enzyme belongs to Peptidase family S8 (subtilisin). The molecular weight of Proteinase K is 28,900 daltons.
IgA protease is an enzyme. This enzyme catalyses the following chemical reaction[reaction equation needed]
Leumorphin, also known as dynorphin B1–29, is a naturally occurring endogenous opioid peptide. Derived as a proteolytic cleavage product of residues 226-254 of prodynorphin, leumorphin is a nonacosapeptide and has the sequence Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Gln-Phe-Lys-Val-Val-Thr-Arg-Ser-Gln-Glu-Asp-Pro-Asn-Ala-Tyr-Ser-Gly-Glu-Leu-Phe-Asp-Ala. It can be further reduced to dynorphin B and dynorphin B-14 by pitrilysin metallopeptidase 1, an enzyme of the endopeptidase family. Leumorphin behaves as a potent and selective κ-opioid receptor agonist, similarly to other endogenous opioid peptide derivatives of prodynorphin.
Aminopeptidase S is an enzyme. This enzyme catalyses the following chemical reaction
Gamma-D-glutamyl-meso-diaminopimelate peptidase is an enzyme. This enzyme catalyses the following chemical reaction
Glutamyl endopeptidase is an extracellular bacterial serine protease of the glutamyl endopeptidase I family that was initially isolated from the Staphylococcus aureus strain V8. The protease is, hence, commonly referred to as "V8 protease", or alternatively SspA from its corresponding gene.
Nuclear-inclusion-a endopeptidase is a protease enzyme found in potyviruses. This enzyme catalyses the following chemical reaction:
Aspergilloglutamic peptidase, also called aspergillopepsin II is a proteolytic enzyme. The enzyme was previously thought be an aspartic protease, but it was later shown to be a glutamic protease with a catalytic Glu residue at the active site, and was therefore renamed aspergilloglutamic peptidase.
Scytalidocarboxyl peptidase B, also known as Scytalidoglutamic peptidase and Scytalidopepsin B is a proteolytic enzyme. It was previously thought to be an aspartic protease, but determination of its molecular structure showed it to belong a novel group of proteases, glutamic protease.
Peptidyl-Asp metalloendopeptidase is an enzyme. This enzyme catalyses the following chemical reaction
Glutamic proteases are a group of proteolytic enzymes containing a glutamic acid residue within the active site. This type of protease was first described in 2004 and became the sixth catalytic type of protease. Members of this group of protease had been previously assumed to be an aspartate protease, but structural determination showed it to belong to a novel protease family. The first structure of this group of protease was scytalidoglutamic peptidase, the active site of which contains a catalytic dyad, glutamic acid (E) and glutamine (Q), which give rise to the name eqolisin. This group of proteases are found primarily in pathogenic fungi affecting plant and human.
Glutamyl endopeptidase I is a family of extracellular bacterial serine proteases. The proteases within this family have been identified in species of Staphylococcus, Bacillus, and Streptomyces, among others. The two former are more closely related, while the Streptomyces-type is treated as a separate family, glutamyl endopeptidase II.
The sedolisin family of peptidases are a family of serine proteases structurally related to the subtilisin (S8) family. Well-known members of this family include sedolisin ("pseudomonalisin") found in Pseudomonas bacteria, xanthomonalisin ("sedolisin-B"), physarolisin as well as animal tripeptidyl peptidase I. It is also known as sedolysin or serine-carboxyl peptidase. This group of enzymes contains a variation on the catalytic triad: unlike S8 which uses Ser-His-Asp, this group runs on Ser-Glu-Asp, with an additional acidic residue Asp in the oxyanion hole.
References
- ↑ Yoshida N, Tsuruyama S, Nagata K, Hirayama K, Noda K, Makisumi S (September 1988). "Purification and characterization of an acidic amino acid specific endopeptidase of Streptomyces griseus obtained from a commercial preparation (Pronase)". Journal of Biochemistry. 104 (3): 451–6. PMID 3149277.
- ↑ Komiyama T, Bigler TL, Yoshida N, Noda K, Laskowski M (June 1991). "Replacement of P1 Leu18 by Glu18 in the reactive site of turkey ovomucoid third domain converts it into a strong inhibitor of Glu-specific Streptomyces griseus proteinase (GluSGP)". The Journal of Biological Chemistry. 266 (17): 10727–30. PMID 1674942.
- ↑ Nagata K, Yoshida N, Ogata F, Araki M, Noda K (December 1991). "Subsite mapping of an acidic amino acid-specific endopeptidase from Streptomyces griseus, GluSGP, and protease V8". Journal of Biochemistry. 110 (6): 859–62. PMID 1794975.
- ↑ Svendsen I, Jensen MR, Breddam K (November 1991). "The primary structure of the glutamic acid-specific protease of Streptomyces griseus". FEBS Letters. 292 (1–2): 165–7. doi: 10.1016/0014-5793(91)80859-2 . PMID 1959600.
- ↑ Breddam K, Meldal M (May 1992). "Substrate preferences of glutamic-acid-specific endopeptidases assessed by synthetic peptide substrates based on intramolecular fluorescence quenching". European Journal of Biochemistry. 206 (1): 103–7. doi: 10.1111/j.1432-1033.1992.tb16906.x . PMID 1587264.
