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QuickView for Pyridoxal-phosphate binding site (biogroup)
- 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; histidine decarboxylase, which catalyses the decarboxylation of histidine to histamine; and L-aspartate decarboxylase, which converts aspartate to beta-alanine. 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).
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