Everything about Protease totally explained
A
protease is any
enzyme that conducts
proteolysis, that is, begins protein
catabolism by
hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain.
Classification
Proteases are
currently classified into six groups:
The threonine and glutamic acid proteases were not described until
1995 and
2004, respectively. The mechanism used to cleave a peptide bond involves making an amino acid residue that has the cysteine and threonine (peptidases) or a water molecule (aspartic acid, metallo- and glutamic acid peptidases) nucleophilic so that it can attack the peptide
carbonyl group. One way to make a nucleophile is by a
catalytic triad, where a
histidine residue is used to activate
serine,
cysteine, or
threonine as a nucleophile.
Occurrence
Proteases occur naturally in all organisms. These enzymes are involved in a multitude of physiological reactions from simple digestion of food proteins to highly-regulated cascades (for example, the
blood-clottin
cascade, the
complement system,
apoptosis pathways, and the invertebrate prophenoloxidase-activating cascade). Peptidases can either break specific peptide bonds (
limited proteolysis), depending on the
amino acid sequence of a protein, or break down a complete peptide to amino acids (
unlimited proteolysis). The activity can be a destructive change, abolishing a protein's function or digesting it to its principal components; it can be an activation of a function, or it can be a signal in a signaling pathway.
Bacterium also secrete proteases to hydrolyse the peptide bonds in proteins and therefore break the proteins down into their constituent monomers.
Proteases are also a type of exotoxin, which is a virulence factor in bacteria pathogenesis. Bacteria exotoxic proteases destroy extracellular structures. Protease enzymes are also found used extensively in the bread industry in
Bread improver.
Proteases, also known as proteinases or proteolytic enzymes, are a large group of
enzymes. Proteases belong to the class of enzymes known as
hydrolases, which catalyse the reaction of
hydrolysis of various bonds with the participation of a water molecule.
Proteases are involved in digesting long protein chains into short fragments, splitting the
peptide bonds that link
amino acid residues. Some of them can detach the terminal amino acids from the protein chain (
exopeptidases, such as
aminopeptidases,
carboxypeptidase
A); the others attack internal peptide bonds of a protein (
endopeptidases, such as trypsin, chymotrypsin, pepsin, papain, elastase).
Proteases are divided into four major groups according to the character of their catalytic
active site and conditions of action: serine proteinases, cysteine (thiol) proteinases, aspartic proteinases, and
metalloproteinases. Attachment of a protease to a certain group depends on the structure of catalytic site and the amino acid (as one of the constituents) essential for its activity.
Proteases are used throughout an organism for various metabolic processes. Acid proteases secreted into the stomach (such as
pepsin) and serine proteases present in
duodenum (
trypsin and
chymotrypsin) enable us to digest the protein in food; proteases present in blood serum (
thrombin,
plasmin,
Hageman factor, etc.) play important role in blood-clotting, as well as lysis of the clots, and the correct action of the immune system. Other proteases are present in leukocytes (
elastase,
cathepsin G) and play several different roles in metabolic control. Proteases determine the lifetime of other proteins playing important physiological role like hormones, antibodies, or other enzymes -- this is one of the fastest "switching on" and "switching off" regulatory mechanisms in the physiology of an organism.
By complex cooperative action the proteases may proceed as
cascade reactions, which result in rapid and efficient amplification of an organism's response to a physiological signal.
Inhibitors
The function of peptidases is inhibited by
protease inhibitor enzymes. Examples of protease inhibitors are the class of
serpins (
serine
protease or
peptidase
inhibitors), incorporating
alpha 1-antitrypsin. Other serpins are
complement 1-inhibitor,
antithrombin,
alpha 1-antichymotrypsin,
plasminogen activator inhibitor 1 (
coagulation,
fibrinolysis) and the recently discovered
neuroserpin.
Natural protease inhibitors include the family of
lipocalin proteins, which play a role in cell regulation and differentiation.
Lipophilic ligands, attached to lipocalin proteins, have been found to possess tumor protease inhibiting properties. The natural
protease inhibitors are not to be confused with the
protease inhibitors used in antiretroviral therapy. Some
viruses, with
HIV among them, depend on proteases in their reproductive cycle. Thus,
protease inhibitors are developed as
antiviral means.
Degradation
Proteases, being themselves proteins, are known to be cleaved by other protease molecules, sometimes of the same variety. This may be an important method of regulation of peptidase activity.
Protease research
The field of protease research is enormous. Barrett and Rawlings estimated that approximately 8000 papers related to this field are published each year. For a look at current activities and interests of protease researchers, see the
International Proteolysis Society
web page.
Further Information
Get more info on 'Protease'.
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