Protease -Creative Enzymes:

Proteases, also called peptidase or proteinase, are a kind of simple destructive enzymes necessary for protein catabolism and the generation of amino acids in primitive organisms by hydrolyzing peptide bonds. Proteases are likely to arise at the earliest stages of protein evolution and have been applied for multiple times. Different classes of protease usually perform the same proteolysis reaction through completely different catalytic mechanisms. Proteases can be found in a wild of sources like animalia, plantae, fungi, bacteria, archaea and viruses and they participate in many body processes including digestion, immune system function, and blood circulation.

Classification Based on catalytic residue, proteases can be classified into seven broad groups: serine proteases, cysteine proteases, threonine proteases, aspartic proteases, glutamic proteases, metalloproteases, and asparagine peptide lyases with an asparagine to perform an elimination reaction (no need of water).

Actually, proteases are primarily grouped into 84 families according to their evolutionary relationship and classified under four catalytic types: serine, cysteine, aspartic, and metallo proteases. It is until 1995 and 2004 respectively that the threonine and glutamic-acid proteases are described. Asparagine peptide lyase as the seventh catalytic type of proteolytic enzymes is described in 2011. Its proteolytic mechanism is unusual since it executes an elimination reaction, during which the catalytic asparagine forms a cyclic chemical structure that cleaves itself at asparagine residues in proteins under the appropriate conditions. Thanks to the fundamentally different mechanism, it is debatable to include peptide lyase as a peptidase. Alternatively, proteases may also be classified based on the optimal pH at which they are active. Acid proteases, basic proteases (or alkaline proteases) and neutral proteases involved in type 1 hypersensitivity can be found according to this classification method. Another up-todate classification of protease evolutionary superfamilies could be found in the MEROPS database, where proteases are classified firstly by 'clan' (superfamily) based on structure, mechanism and catalytic residue order. Within each 'clan', proteases are further classified into families on the basis of sequence similarity and each family may have hundreds of related proteases. Up to now, more than 50 clans are known, each one of which indicates an independent evolutionary origin of proteolysis.

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