Protease

proteasespeptidaseproteinaseproteolytic enzymeproteolytic cleavageproteolytic enzymespeptidasesproteinasesproteolyticEnzymes that break down proteins
A protease (also called a peptidase or proteinase) is an enzyme that catalyzes (increases the rate of) proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids.wikipedia
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Catalytic triad

triadactive sitecatalytic tryad
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. This is not an evolutionary grouping, however, as the nucleophile types have evolved convergently in different superfamilies, and some superfamilies show divergent evolution to multiple different nucleophiles.
Catalytic triads are most commonly found in hydrolase and transferase enzymes (e.g. proteases, amidases, esterases, acylases, lipases and β-lactamases).

Protein catabolism

protein breakdownbreakdown of proteinsbroken down
Proteases are involved in many biological functions, including digestion of eaten proteins, protein catabolism (breakdown of old proteins), and cell signalling.
Protein catabolism is most commonly carried out by non-specific endo- and exo-proteases.

Enzyme

enzymologyenzymesenzymatic
A protease (also called a peptidase or proteinase) is an enzyme that catalyzes (increases the rate of) proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids.
Enzymes such as amylases and proteases break down large molecules (starch or proteins, respectively) into smaller ones, so they can be absorbed by the intestines.

Cysteine protease

cysteinecysteine peptidasecysteine endopeptidase
These proteases share a common catalytic mechanism that involves a nucleophilic cysteine thiol in a catalytic triad or dyad.

Aspartic protease

aspartyl proteaseaspartic proteasesaspartic proteinase
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.

Protein superfamily

superfamilysuperfamiliesprotein fold
This is not an evolutionary grouping, however, as the nucleophile types have evolved convergently in different superfamilies, and some superfamilies show divergent evolution to multiple different nucleophiles. In this database, proteases are classified firstly by 'clan' (superfamily) based on structure, mechanism and catalytic residue order (e.g. the PA clan where P indicates a mixture of nucleophile families).
The term protein clan is commonly used for protease and glycosyl hydrolases superfamilies based on the MEROPS and CAZy classification systems.

Metalloproteinase

metalloproteasemetalloproteinasesmetallopeptidase
A metalloproteinase, or metalloprotease, is any protease enzyme whose catalytic mechanism involves a metal.

Asparagine peptide lyase

Asparagine peptide lyases
Asparagine peptide lyase are one of the seven groups in which proteases, also termed proteolytic enzymes, peptidases, or proteinases, are classified according to their catalytic residue.

Convergent evolution

convergentconvergenceanalogous
They have independently evolved multiple times, and different classes of protease can perform the same reaction by completely different catalytic mechanisms.
The enzymology of proteases provides some of the clearest examples of convergent evolution.

PA clan of proteases

PA clanPAPA superfamily
In this database, proteases are classified firstly by 'clan' (superfamily) based on structure, mechanism and catalytic residue order (e.g. the PA clan where P indicates a mixture of nucleophile families).
The PA clan (Proteases of mixed nucleophile, superfamily A) is the largest group of proteases with common ancestry as identified by structural homology.

Elastase

neutrophil elastase
Each family may contain many hundreds of related proteases (e.g. trypsin, elastase, thrombin and streptogrisin within the S1 family). Some detach the terminal amino acids from the protein chain (exopeptidases, such as aminopeptidases, carboxypeptidase A); others attack internal peptide bonds of a protein (endopeptidases, such as trypsin, chymotrypsin, pepsin, papain, elastase).
In molecular biology, elastase is an enzyme from the class of proteases (peptidases) that break down proteins.

Glutamic protease

glutamic-
This type of protease was first described in 2004 and became the sixth catalytic type of protease.

Calpain

calpains
A calpain is a protein belonging to the family of calcium-dependent, non-lysosomal cysteine proteases (proteolytic enzymes) expressed ubiquitously in mammals and many other organisms.

Enzyme catalysis

catalytic mechanisminduced fitenzymatic reaction
They have independently evolved multiple times, and different classes of protease can perform the same reaction by completely different catalytic mechanisms.
This mechanism is utilised by the catalytic triad of enzymes such as proteases like chymotrypsin and trypsin, where an acyl-enzyme intermediate is formed.

Complement system

complementcomplement cascadecomplement activation
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).
When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cleavages.

Exopeptidase

exopeptidases
Some detach the terminal amino acids from the protein chain (exopeptidases, such as aminopeptidases, carboxypeptidase A); others attack internal peptide bonds of a protein (endopeptidases, such as trypsin, chymotrypsin, pepsin, papain, elastase).
An exopeptidase is any peptidase that catalyzes the cleavage of the terminal (or the penultimate) peptide bond; the process releases a single amino acid or dipeptide from the peptide chain.

Cell signaling

cell signallingsignallingsignaling pathway
Proteases are involved in many biological functions, including digestion of eaten proteins, protein catabolism (breakdown of old proteins), and cell signalling.
As shown in Figure 2, activation of Notch can cause the Notch protein to be altered by a protease.

Endopeptidase

endopeptidasesendoproteaseendopeptidase clp
Some detach the terminal amino acids from the protein chain (exopeptidases, such as aminopeptidases, carboxypeptidase A); others attack internal peptide bonds of a protein (endopeptidases, such as trypsin, chymotrypsin, pepsin, papain, elastase).
Endopeptidase or endoproteinase are proteolytic peptidases that break peptide bonds of nonterminal amino acids (i.e. within the molecule), in contrast to exopeptidases, which break peptide bonds from end-pieces of terminal amino acids.

Trypsin

trypticanti-tryptictrypsin serine proteases
Each family may contain many hundreds of related proteases (e.g. trypsin, elastase, thrombin and streptogrisin within the S1 family). Some detach the terminal amino acids from the protein chain (exopeptidases, such as aminopeptidases, carboxypeptidase A); others attack internal peptide bonds of a protein (endopeptidases, such as trypsin, chymotrypsin, pepsin, papain, elastase).
Once in the small intestine, the enzyme enteropeptidase activates trypsinogen into trypsin by proteolytic cleavage.

Protein

proteinsproteinaceousstructural proteins
A protease (also called a peptidase or proteinase) is an enzyme that catalyzes (increases the rate of) proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids.
Ingested proteins are then broken down into amino acids through digestion, which typically involves denaturation of the protein through exposure to acid and hydrolysis by enzymes called proteases.

Rennet

animal rennetenzymeFermentation-Produced Chymosin
Protease containing plant-solutions called vegetarian rennet has been in use for hundreds of years in Europe and middle-east for making kosher and halal Cheeses.
Chymosin, its key component, is a protease enzyme that curdles the casein in milk.

Apoptosis

apoptoticprogrammed cell deathcell death
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).
Both pathways induce cell death by activating caspases, which are proteases, or enzymes that degrade proteins.

Proteasome

proteasomalproteosomeproteasomes
Bacteria contain proteases responsible for general protein quality control (e.g. the AAA+ proteasome) by degrading unfolded or misfolded proteins.
Enzymes that help such reactions are called proteases.

Snake venom

venomsnake venomsvenomous
Some snake venoms are also proteases, such as pit viper haemotoxin and interfere with the victim's blood clotting cascade.
Amino acid oxidases and proteases are used for digestion.