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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.
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.
Tissue kallikrein is an enzyme. This enzyme catalyses the following chemical reaction
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.
Ovomucoid is a protein found in egg whites. It is a trypsin inhibitor with three protein domains of the Kazal domain family. The homologs from chickens and especially turkeys are best characterized. It is not related to the similarly named ovomucin, another egg white protein.
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.
Pancreatic secretory trypsin inhibitor (PSTI) also known as serine protease inhibitor Kazal-type 1 (SPINK1) or tumor-associated trypsin inhibitor (TATI) is a protein that in humans is encoded by the SPINK1 gene.
In molecular biology the protein SSI is a Subtilisin inhibitor-like which stands for Streptomyces subtilisin inhibitor. This is a protease inhibitor. These are often synthesised as part of a larger precursor protein, either as a prepropeptide. The function of this protein domain is to prevent access of the substrate to the active site. It is found only in bacteria.
In molecular biology, the Bowman–Birk protease inhibitor family of proteins consists of eukaryotic proteinase inhibitors, belonging to MEROPS inhibitor family I12, clan IF. They mainly inhibit serine peptidases of the S1 family, but also inhibit S3 peptidases.
The Kazal domain is an evolutionary conserved protein domain usually indicative of serine protease inhibitors. However, kazal-like domains are also seen in the extracellular part of agrins, which are not known to be protease inhibitors.
Antipain is an oligopeptide that is isolated from actinomycetes and used in biochemical research as a protease inhibitor of trypsin and papain. It was discovered in 1972 and was the first natural peptide found that contained an ureylene group. Antipain can aid in prevention of coagulation in blood. It is an inhibitor of serine and cysteine proteases.
Alpha-lytic endopeptidase or Alpha-lytic protease is an enzyme isolated from the myxobacterium Lysobacter enzymogenes. This enzyme is a serine protease that catalyses the breakage of peptide bonds using a hydrolysis chemical reaction. Alpha-lytic protease was named based on the observed cleavage specificity for the α position of the tetrapeptide component in gram-positive bacterial cell walls (alanine). Alpha-lytic protease is also capable of digesting elastin and other proteins.
Thermitase is an enzyme. This enzyme catalyses the following chemical reaction
Streptogrisin A is an enzyme. This enzyme catalyses the following chemical reaction
Glutamyl endopeptidase II is an enzyme. This enzyme catalyses the following chemical reaction
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.
The PA clan is the largest group of proteases with common ancestry as identified by structural homology. Members have a chymotrypsin-like fold and similar proteolysis mechanisms but can have identity of <10%. The clan contains both cysteine and serine proteases. PA clan proteases can be found in plants, animals, fungi, eubacteria, archaea and viruses.
Randy John Read is a Wellcome Trust Principal Research Fellow and professor of protein crystallography at the University of Cambridge.
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.
References
- ↑ Jurasek L, Fackre D, Smillie LB (September 1969). "Remarkable homology about the disulfide bridges of a trypsin-like enzyme from Streptomyces griseus". Biochemical and Biophysical Research Communications. 37 (1): 99–105. doi:10.1016/0006-291x(69)90885-7. PMID 4899581.
- ↑ Fujinaga M, Read RJ, Sielecki A, Ardelt W, Laskowski M, James MN (August 1982). "Refined crystal structure of the molecular complex of Streptomyces griseus protease B, a serine protease, with the third domain of the ovomucoid inhibitor from turkey". Proceedings of the National Academy of Sciences of the United States of America. 79 (16): 4868–72. doi: 10.1073/pnas.79.16.4868 . PMC 346786 . PMID 6750612.
- ↑ Read RJ, Fujinaga M, Sielecki AR, James MN (September 1983). "Structure of the complex of Streptomyces griseus protease B and the third domain of the turkey ovomucoid inhibitor at 1.8-A resolution". Biochemistry. 22 (19): 4420–33. doi:10.1021/bi00288a012. PMID 6414511.
- ↑ Henderson G, Krygsman P, Liu CJ, Davey CC, Malek LT (August 1987). "Characterization and structure of genes for proteases A and B from Streptomyces griseus". Journal of Bacteriology. 169 (8): 3778–84. doi:10.1128/jb.169.8.3778-3784.1987. PMC 212465 . PMID 3112129.
- ↑ Greenblatt HM, Ryan CA, James MN (January 1989). "Structure of the complex of Streptomyces griseus proteinase B and polypeptide chymotrypsin inhibitor-1 from Russet Burbank potato tubers at 2.1 A resolution". Journal of Molecular Biology. 205 (1): 201–28. doi:10.1016/0022-2836(89)90376-8. PMID 2494344.
