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.
Serine proteases are enzymes that cleave peptide bonds in proteins. 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.
A metalloproteinase, or metalloprotease, is any protease enzyme whose catalytic mechanism involves a metal. An example is ADAM12 which plays a significant role in the fusion of muscle cells during embryo development, in a process known as myogenesis.
Subtilisin is a protease initially obtained from Bacillus subtilis.
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.
The heat shock proteins HslV and HslU are expressed in many bacteria such as E. coli in response to cell stress. The hslV protein is a protease and the hslU protein is an ATPase; the two form a symmetric assembly of four stacked rings, consisting of an hslV dodecamer bound to an hslU hexamer, with a central pore in which the protease and ATPase active sites reside. The hslV protein degrades unneeded or damaged proteins only when in complex with the hslU protein in the ATP-bound state. HslV is thought to resemble the hypothetical ancestor of the proteasome, a large protein complex specialized for regulated degradation of unneeded proteins in eukaryotes, many archaea, and a few bacteria. HslV bears high similarity to core subunits of proteasomes.
The enzyme Acid-Induced Arginine Decarboxylase (AdiA), also commonly referred to as arginine decarboxylase, catalyzes the conversion of L-arginine into agmatine and carbon dioxide. The process consumes a proton in the decarboxylation and employs a pyridoxal-5'-phosphate (PLP) cofactor, similar to other enzymes involved in amino acid metabolism, such as ornithine decarboxylase and glutamine decarboxylase. It is found in bacteria and virus, though most research has so far focused on forms of the enzyme in bacteria. During the AdiA catalyzed decarboxylation of arginine, the necessary proton is consumed from the cell cytoplasm which helps to prevent the over-accumulation of protons inside the cell and serves to increase the intracellular pH. Arginine decarboxylase is part of an enzymatic system in Escherichia coli, Salmonella Typhimurium, and methane-producing bacteria Methanococcus jannaschii that makes these organisms acid resistant and allows them to survive under highly acidic medium.
Serine protease HTRA2, mitochondrial is an enzyme that in humans is encoded by the HTRA2 gene. This protein is involved in caspase-dependent apoptosis and in Parkinson's disease.
ATP-dependent Clp protease proteolytic subunit (ClpP) is an enzyme that in humans is encoded by the CLPP gene. This protein is an essential component to form the protein complex of Clp protease.
In molecular biology, the CLP protease family is a family of serine peptidases belong to the MEROPS peptidase family S14. ClpP is an ATP-dependent protease that cleaves a number of proteins, such as casein and albumin. It exists as a heterodimer of ATP-binding regulatory A and catalytic P subunits, both of which are required for effective levels of protease activity in the presence of ATP, although the P subunit alone does possess some catalytic activity.
OmpT is an aspartyl protease found on the outer membrane of Escherichia coli. OmpT is a subtype of the family of omptin proteases, which are found on some gram-negative species of bacteria.
Peptidyl-dipeptidase Dcp (EC 3.4.15.5, dipeptidyl carboxypeptidase (Dcp), dipeptidyl carboxypeptidase) is a metalloenzyme found in the cytoplasm of bacterium E. Coli responsible for the C-terminal cleavage of a variety of dipeptides and unprotected larger peptide chains. The enzyme does not hydrolyze bonds in which P1' is Proline, or both P1 and P1' are Glycine. Dcp consists of 680 amino acid residues that form into a single active monomer which aids in the intracellular degradation of peptides. Dcp coordinates to divalent zinc which sits in the pocket of the active site and is composed of four subsites: S1’, S1, S2, and S3, each subsite attracts certain amino acids at a specific position on the substrate enhancing the selectivity of the enzyme. The four subsites detect and bind different amino acid types on the substrate peptide in the P1 and P2 positions. Some metallic divalent cations such as Ni+2, Cu+2, and Zn+2 inhibit the function of the enzyme around 90%, whereas other cations such as Mn+2, Ca+2, Mg+2, and Co+2 have slight catalyzing properties, and increase the function by around 20%. Basic amino acids such as Arginine bind preferably at the S1 site, the S2 site sits deeper in the enzyme therefore is restricted to bind hydrophobic amino acids with phenylalanine in the P2 position. Dcp is divided into two subdomains (I, and II), which are the two sides of the clam shell-like structure and has a deep inner cavity where a pair of histidine residues bind to the catalytic zinc ion in the active site. Peptidyl-Dipeptidase Dcp is classified like Angiotensin-I converting enzyme (ACE) which is also a carboxypeptidase involved in blood pressure regulation, but due to structural differences and peptidase activity between these two enzymes they had to be examined separately. ACE has endopeptidase activity, whereas Dcp strictly has exopeptidase activity based on its cytoplasmic location and therefore their mechanisms of action are differentiated. Another difference between these enzymes is that the activity of Peptidyl-Dipeptidase Dcp is not enhanced in the presence of chloride anions, whereas chloride enhances ACE activity.
Endopeptidase So is an enzyme. This enzyme catalyses the following chemical reaction
Signal peptidase I is an enzyme. This enzyme catalyses the following chemical reaction
HtrA2 peptidase is an enzyme. This enzyme catalyses the following chemical reaction
C5a peptidase is an enzyme. The primary cleavage site is at His67-Lys68 in human C5a with a minor secondary cleavage site at Ala58-Ser59.
Serralysin is an enzyme. This enzyme catalyses the following chemical reaction
Oligopeptidase A is an enzyme. This enzyme catalyses the following chemical reaction
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.
ATP-dependent Clp protease ATP-binding subunit clpX-like, mitochondrial is an enzyme that in humans is encoded by the CLPX gene. This protein is a member of the family of AAA Proteins and is to form the protein complex of Clp protease.
