Information AboutProtease |
| CATEGORIES ABOUT PROTEASE | |
| ec 3.4 | |
| posttranslational modification | |
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CLASSIFICATION There are Currently six classes of proteases:
The threonine and glutamic peptidases were not described until 1995 and 2004 , respectively. The mechanism used to cleave a peptide bond involves making an amino acid residue (serine, cystein and threonine peptidases) or a water molecule (aspartic, metallo and glutamic 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 and constitute 1-5% of the gene content. These enzymes are involved in a multitude of physiological reactions from simple digestion of food proteins to highly regulated cascades (e.g. the Blood Clotting Cascade , the Complement System , Apoptosis pathways, and the invertebrate prophenoloxidase activating cascade). Peptidases can break either 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 signalling pathway. INHIBITORS The function of peptidases is inhibited by Protease Inhibitor enzymes. Examples of protease inhibitors are the class of Serpin s (''ser''ine ''p''rotease or ''p''eptidase ''in''hibitors), 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 . The natural Protease Inhibitor s are not to be confused with the Protease Inhibitor s used in antiretroviral therapy. Some Virus es, with HIV among them, depend on proteases in their reproductive cycle. Thus, Protease Inhibitor s 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. REFERENCES
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