A protease is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids. 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.
Serine proteases are enzymes that cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the (enzyme's) active site. They are found ubiquitously in both eukaryotes and prokaryotes. Serine proteases fall into two broad categories based on their structure: chymotrypsin-like (trypsin-like) or subtilisin-like.
Cysteine proteases, also known as thiol proteases, are enzymes that degrade proteins. These proteases share a common catalytic mechanism that involves a nucleophilic cysteine thiol in a catalytic triad or dyad.
The cystatins are a family of cysteine protease inhibitors which share a sequence homology and a common tertiary structure of an alpha helix lying on top of an anti-parallel beta sheet. The family is subdivided as described below.
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.
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.
Serine protease HTRA1 is an enzyme that in humans is encoded by the HTRA1 gene. The HTRA1 protein is composed of four distinct protein domains. They are from amino-terminus to carboxyl-terminus an Insulin-like growth factor binding domain, a kazal domain, a trypsin-like peptidase domain and a PDZ domain.
Lympho-epithelial Kazal-type-related inhibitor (LEKTI) also known as serine protease inhibitor Kazal-type 5 (SPINK5) is a protein that in humans is encoded by the SPINK5 gene.
Serpin B6 is a protein that in humans is encoded by the SERPINB6 gene.
Serine protease inhibitor Kazal-type 2 also known as acrosin-trypsin inhibitor is a protein that in humans is encoded by the SPINK2 gene.
Kunitz soybean trypsin inhibitor is a type of protein contained in legume seeds which functions as a protease inhibitor. Kunitz-type Soybean Trypsin Inhibitors are usually specific for either trypsin or chymotrypsin. They are thought to protect seeds against consumption by animal predators.
Kunitz domains are the active domains of proteins that inhibit the function of protein degrading enzymes or, more specifically, domains of Kunitz-type are protease inhibitors. They are relatively small with a length of about 50 to 60 amino acids and a molecular weight of 6 kDa. Examples of Kunitz-type protease inhibitors are aprotinin, Alzheimer's amyloid precursor protein (APP), and tissue factor pathway inhibitor (TFPI).
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.
In molecular biology, ecotin is a protease inhibitor which belongs to MEROPS inhibitor family I11, clan IN. Ecotins are dimeric periplasmic proteins from Escherichia coli and related Gram-negative bacteria that have been shown to be potent inhibitors of many trypsin-fold serine proteases of widely varying substrate specificity, which belong to MEROPS peptidase family S1. Phylogenetic analysis suggested that ecotin has an exogenous target, possibly neutrophil elastase. Ecotin from E. coli, Yersinia pestis, and Pseudomonas aeruginosa, all species that encounter the mammalian immune system, inhibit neutrophil elastase strongly while ecotin from the plant pathogen Pantoea citrea inhibits neutrophil elastase 1000-fold less potently. Ecotins all potently inhibit pancreatic digestive peptidases trypsin and chymotrypsin, while showing more variable inhibition of the blood peptidases Factor Xa, thrombin, and urokinase-type plasminogen activator.
Serine protease inhibitor Kazal-type 6 (SPINK6) is a protein encoded by the SPINK6 gene in humans. It is a potent inhibitor of epidermal proteases involved in maintaining skin homeostasis, including KLK5, KLK7 and KLK14. SPINK6 is a member of a gene family cluster located on chromosome 5q33.1, which includes SPINK5 and SPINK9.
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.
Pacifastin is a family of serine proteinase inhibitors found in arthropods. Pacifastin inhibits the serine peptidases trypsin and chymotrypsin.
