| Type: | Binding_site | Name: | Pyridoxal-phosphate binding site |
| Description: | Pyridoxal phosphate is the active form of vitamin B6 (pyridoxine or pyridoxal). Pyridoxal 5'-phosphate (PLP) is a versatile catalyst, acting as a coenzyme in a multitude of reactions, including decarboxylation, deamination and transamination [, , ]. PLP-dependent enzymes are primarily involved in the biosynthesis of amino acids and amino acid-derived metabolites, but they are also found in the biosynthetic pathways of amino sugars and in the synthesis or catabolism of neurotransmitters; pyridoxal phosphate can also inhibit DNA polymerases and several steroid receptors []. Inadequate levels of pyridoxal phosphate in the brain can cause neurological dysfunction, particularly epilepsy [].PLP enzymes exist in their resting state as a Schiff base, the aldehyde group of PLP forming a linkage with the epsilon-amino group of an active site lysine residue on the enzyme. The alpha-amino group of the substrate displaces the lysine epsilon-amino group, in the process forming a new aldimine with the substrate. This aldimine is the common central intermediate for all PLP-catalysed reactions, enzymatic and non-enzymatic [].A number of pyridoxal-dependent decarboxylases share regions of sequence similarity, particularly in the vicinity of a conserved lysine residue, which provides the attachment site for the pyridoxal-phosphate (PLP) group [, ]. Among these enzymes are aromatic-L-amino-acid decarboxylase (L-dopa decarboxylase or tryptophan decarboxylase), which catalyses the decarboxylation of tryptophan to tryptamine []; tyrosine decarboxylase, which converts tyrosine into tyramine; and histidine decarboxylase, which catalyses the decarboxylation of histidine to histamine []. These enzymes belong to the group II decarboxylases [, ].This signature contains the pyridoxal-phosphate-binding lysine residue. Certain pyridoxal-dependent decarboxylases seem to share regions of sequence similarity [, , , ], especially in the vicinity of the lysine residue which serves as the attachment site for the pyridoxal-phosphate (PLP) group. These enzymes, known collectively as group II decarboxylases, are:Glutamate decarboxylase () (GAD), which catalyses the decarboxylation of glutamate into the neurotransmitter GABA (4-aminobutanoate).Histidine decarboxylase () (HDC), which catalyses the decarboxylation of histidine to histamine. There are two completely unrelated types of HDC: those that use PLP as a cofactor (found in Gram-negative bacteria and mammals), and those that contain a covalently bound pyruvoyl residue (found in Gram-positive bacteria).Aromatic-L-amino-acid decarboxylase ()(DDC; also known as L-dopa decarboxylase or tryptophan decarboxylase), which catalyses the decarboxylation of tryptophan to tryptamine. It also acts on 5-hydroxy-tryptophan and dihydroxyphenylalanine (L-dopa).Tyrosine decarboxylase () (TyrDC), which converts tyrosine into tyramine, a precursor of isoquinoline alkaloids and various amides.Cysteine sulphinic acid decarboxylase ().L-2,4-diaminobutyrate decarboxylase () (DABA decarboxylase). | Short Name: | Pyridoxal-P_BS |
| DB identifier | Type | Name |
|---|---|---|
| IPR015424 | Domain | Pyridoxal phosphate-dependent transferase |
| IPR015421 | Domain | Pyridoxal phosphate-dependent transferase, major region, subdomain 1 |
| IPR002129 | Family | Pyridoxal phosphate-dependent decarboxylase |
| IPR010977 | Family | Aromatic-L-amino-acid decarboxylase |
| IPR022397 | Family | Tyrosine decarboxylase, bacteria |
| IPR020931 | Family | Tyrosine decarboxylase |
