A catalytic triad commonly refers to the three amino acid residues found inside the active site of certain protease enzymes: serine (S), aspartate (D) and histidine (H). In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this The active site of an Enzyme contains the catalytic and Binding sites. A protease is any Enzyme that conducts Proteolysis, that is begins protein Catabolism by Hydrolysis of the Peptide bonds that link Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Serine (abbreviated as Ser or S) is an Organic compound with the formula H[[oxygen O]]2 CCH NH sub>2CH2OH Aspartic acid (abbreviated as Asp or D; Asx or B represent either aspartic acid or Asparagine) is an α- Amino acid Histidine (abbreviated as His or H) is one of the 20 standard Amino acids present in Proteins In the Nutritional sense in They work together to break peptide bonds on polypeptides. Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino More generally, catalytic triad can refer to any set of three residues that function together and are directly involved in catalysis. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Because enzymes fold into complex three-dimensional shapes, the residues of a catalytic triad can be far from each other in the primary structure however are brought close together in the tertiary structure. In Biochemistry, the primary structure of a biological molecule is the exact specification of its atomic composition and the chemical bonds connecting those atoms (including In Biochemistry and Chemistry, the tertiary structure of a Protein or any other Macromolecule is its three-dimensional structure as defined
Example
An example of a catalytic triad is present in chymotrypsin, where the triad (on the enzyme) consists of S195 (that is the serine found at residue 195 in the protein sequence), D102 and H57. Chymotrypsin (bovine γ chymotrypsin,) is a digestive enzyme that can perform Proteolysis. Essentially, S195 binds to the substrate polypeptide to the side of a phenylalanine, tryptophan or tyrosine residue closer to the C-terminus, holding it in place. Phe redirects here For the BitTorrent feature see PHE. For the constellation see Phoenix (constellation. Tryptophan (abbreviated as Trp or W) is one of the 20 standard amino acids, as well as an Essential amino acid in the Human diet Tyrosine (abbreviated as Tyr or Y) or 4-hydroxyphenylalanine, is one of the 20 Amino acids that are used by cells to synthesize The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal end, or D102 and H57 then hydrolyze the bond. This takes place in several steps.
- Upon binding of the target protein, the carboxylic group (-COOH) on D102 forms a low-barrier hydrogen bond with H57, increasing the pKa of its imidazole nitrogen from 7 to about 12. A Low-barrier hydrogen bond or LBHB is a special type of Hydrogen bond. This allows H57 to act as a powerful general base, and deprotonate S195.
- The deprotonated S195 serves as a nucleophile, attacking the carbonyl carbon on the C-terminal side of the residue and forcing the carbonyl oxygen to accept an electron, and transforming the sp2 carbon into a tetrahedral intermediate. In Chemistry, a nucleophile (literally nucleus lover as in nucleus and phile) is a Reagent that forms a Chemical bond to A tetrahedron (plural tetrahedra) is a Polyhedron composed of four triangular faces three of which meet at each vertex. This intermediate is stabilized by an oxanion hole, which also involves S195. An oxanion hole is a pocket in the structure of an Enzyme which stabilizes a deprotonated Oxygen or Alkoxide, often by placing it close to positively
- Collapse of this intermediate back to a carbonyl causes H57 to donate its proton to the nitrogen attached to the alpha carbon. The nitrogen and the attached peptide fragment (c-terminal to the F W or Y residue) leave by diffusion.
- A water molecule then donates a proton to H57 and the remaining OH- attacks the carbonyl carbon, forming another tetrahedral intermediate. The OH is a worse leaving group than the C-terminal fragment, so when the tetrahedral intermediate collapses again, S195 leaves and regains a proton from H57. A leaving group is an Atom or group of atoms that detaches from a chemical substance
- The cleaved peptide, now with a carboxyl end, leaves by diffusion.
See also
References
- Lehninger, Principles of Biochemistry, 4th ed. In Organic chemistry, functional groups are specific groups of Atoms within Molecules that are responsible for the characteristic Chemical reactions (pp 216-219)
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