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 numerous biological pathways, 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 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.
Collagenases are enzymes that break the peptide bonds in collagen. They assist in destroying extracellular structures in the pathogenesis of bacteria such as Clostridium. They are considered a virulence factor, facilitating the spread of gas gangrene. They normally target the connective tissue in muscle cells and other body organs.
Thermolysin is a thermostable neutral metalloproteinase enzyme produced by the Gram-positive bacteria Bacillus thermoproteolyticus. It requires one zinc ion for enzyme activity and four calcium ions for structural stability. Thermolysin specifically catalyzes the hydrolysis of peptide bonds containing hydrophobic amino acids. However thermolysin is also widely used for peptide bond formation through the reverse reaction of hydrolysis. Thermolysin is the most stable member of a family of metalloproteinases produced by various Bacillus species. These enzymes are also termed 'neutral' proteinases or thermolysin -like proteinases (TLPs).
Met-enkephalin, also known as metenkefalin (INN), sometimes referred to as opioid growth factor (OGF), is a naturally occurring, endogenous opioid peptide that has opioid effects of a relatively short duration. It is one of the two forms of enkephalin, the other being leu-enkephalin. The enkephalins are considered to be the primary endogenous ligands of the δ-opioid receptor, due to their high potency and selectivity for the site over the other endogenous opioids.
Neprilysin is an enzyme that in humans is encoded by the MME gene. Neprilysin is a zinc-dependent metalloprotease that cleaves peptides at the amino side of hydrophobic residues and inactivates several peptide hormones including glucagon, enkephalins, substance P, neurotensin, oxytocin, and bradykinin. It also degrades the amyloid beta peptide whose abnormal folding and aggregation in neural tissue has been implicated as a cause of Alzheimer's disease. Synthesized as a membrane-bound protein, the neprilysin ectodomain is released into the extracellular domain after it has been transported from the Golgi apparatus to the cell surface.
Glutamyl aminopeptidase (EC 3.4.11.7, aminopeptidase A, aspartate aminopeptidase, angiotensinase A, glutamyl peptidase, Ca2+-activated glutamate aminopeptidase, membrane aminopeptidase II, antigen BP-1/6C3 of mouse B lymphocytes, L-aspartate aminopeptidase, angiotensinase A2) is an enzyme encoded by the ENPEP gene. Glutamyl aminopeptidase has also recently been designated CD249 (cluster of differentiation 249).
Urodilatin (URO) is a hormone that causes natriuresis by increasing renal blood flow. It is secreted in response to increased mean arterial pressure and increased blood volume from the cells of the distal tubule and collecting duct. It is important in oliguric patients as it lowers serum creatinine and increases urine output.
Racecadotril, also known as acetorphan, is an antidiarrheal medication which acts as a peripheral enkephalinase inhibitor. Unlike other opioid medications used to treat diarrhea, which reduce intestinal motility, racecadotril has an antisecretory effect — it reduces the secretion of water and electrolytes into the intestine. It is available in France and other European countries as well as most of South America and some South East Asian countries, but not in the United States. It is sold under the tradename Hidrasec, among others. Thiorphan is the active metabolite of racecadotril, which exerts the bulk of its inhibitory actions on enkephalinases.
Enkephalinases are enzymes that degrade endogenous enkephalin opioid peptides. They include:
Candoxatril is the orally active prodrug of candoxatrilat (UK-73967).
An Oligopeptidase is an enzyme that cleaves peptides but not proteins. This property is due to its structure: the active site of this enzyme is located at the end of a narrow cavity which can only be reached by peptides.
Astacins are a family of multidomain metalloendopeptidases which are either secreted or membrane-anchored. These metallopeptidases belong to the MEROPS peptidase family M12, subfamily M12A. The protein fold of the peptidase domain for members of this family resembles that of thermolysin, the type example for clan MA and the predicted active site residues for members of this family and thermolysin occur in the motif HEXXH.
Kelatorphan is a drug which acts as a powerful and complete inhibitor of nearly all of the enzymes responsible for catabolism of the endogenous enkephalins, including neutral endopeptidase (NEP), dipeptidyl peptidase III (DPP3), aminopeptidase N (APN), and angiotensin-converting enzyme (ACE). In mice, with the intracerebroventricular co-administration of a 50 μg dose of kelatorphan (this route is necessary because kelatorphan is incapable of crossing the blood-brain-barrier) hence alongside exogenous [Met]enkephalin (ED50 approximately 10 ng), it potentiated the analgesic effects of the latter by 50,000 times. Kelatorphan also displays potent antinociceptive effects alone, and does not depress respiration, although at high doses it actually increases it.
Spinorphin is an endogenous, non-classical opioid peptide of the hemorphin family first isolated from the bovine spinal cord (hence the prefix spin-) and acts as a regulator of the enkephalinases, a class of enzymes that break down endogenous the enkephalin peptides. It does so by inhibiting the enzymes aminopeptidase N (APN), dipeptidyl peptidase III (DPP3), angiotensin-converting enzyme (ACE), and neutral endopeptidase (NEP). Spinorphin is a heptapeptide and has the amino acid sequence Leu-Val-Val-Tyr-Pro-Trp-Thr (LVVYPWT). It has been observed to possess antinociceptive, antiallodynic, and anti-inflammatory properties. The mechanism of action of spinorphin has not been fully elucidated (i.e., how it acts to inhibit the enkephalinases), but it has been found to act as an antagonist of the P2X3 receptor, and as a weak partial agonist/antagonist of the FP1 receptor.
Tynorphin is a synthetic opioid peptide which is a potent and competitive inhibitor of the enkephalinase class of enzymes which break down the endogenous enkephalin peptides. It specifically inactivates dipeptidyl aminopeptidase III (DPP3) with very high efficacy, but also inhibits neutral endopeptidase (NEP), aminopeptidase N (APN), and angiotensin-converting enzyme (ACE) to a lesser extent. It has a pentapeptide structure with the amino acid sequence Val-Val-Tyr-Pro-Trp (VVYPW).
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.
An endopeptidase inhibitor is a drug that inhibits one or more endopeptidase enzymes. Endopeptidases are one of two types of proteases, the other being exopeptidases. Endopeptidases cleave peptide bonds of non-terminal amino acids, whereas exopeptidases break terminal bonds, resulting in the release of a single amino acid or dipeptide from the peptide chain.
Thimet oligopeptidases, also known as TOPs, are a type of M3 metallopeptidases. These enzymes can be found in animals and plants, showing distinctive functions. In animals and humans, they are involved in the degradation of peptides, such as bradykinin, neurotensin, angiotensin I, and Aβ peptide, helping to regulate physiological processes. In plants, their role is related to the degradation of targeting peptides and the immune response to pathogens through Salicylic Acid (SA)-dependent stress signaling. In Arabidopsis thaliana—recognized as a model plant for scientific studies—two thimet oligopeptidases, known as TOP1 and TOP2, have been identified as targets for salicylic acid binding in the plant. These TOP enzymes are key components to understand the SA-mediated signaling where interactions exist with different components and most of the pathways are unknown.
