Flavonol 3-O-glucosyltransferase

Flavonol 3-O-glucosyltransferase
Flavonol 3-O-glucosyltransferase
Identifiers
EC no.	2.4.1.91
CAS no.	50812-18-5
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / QuickGO
Search PMC articles PubMed articles NCBI proteins

In enzymology, a flavonol 3-O-glucosyltransferase (EC 2.4.1.91) is an enzyme that catalyzes the chemical reaction

UDP-glucose + a flavonol ${\displaystyle \rightleftharpoons }$ UDP + a flavonol 3-O-beta-D-glucoside

Thus, the two substrates of this enzyme are UDP-glucose and flavonol, whereas its two products are UDP and flavonol 3-O-beta-D-glucoside. The flavonoids that can act as substrates within this reaction include quercetin, kaempferol, dihydrokaempferol, kaempferid, fisetin, and isorhamnetin. Flavonol 3-O-glucosyltransferase is a hexosyl group transfer enzyme.^[1]

This enzyme is known by the systematic name UPD-glucose:flavonol 3-O-D glucosyltransferase, and it participates in flavonoid biosynthesis and causes the formation of anthocyanins. Anthocyanins produce a purple color in the plant tissues that they are present in.^[2]

It is an enzyme found most notably in grapes (Vitis vinifera).^[3] This enzyme is found within a number of other plants as well—such as snapdragons (Antirrhinum majus), kale (Brassica oleracea), and grapefruit (Citrus x paradisi).^[4]

This enzyme is involved in the biosynthesis of secondary metabolites. The primary function of this enzyme within its pathway is binding a glucoside onto a flavonol molecule, forming a flavonol 3-O-glucoside.^[5] It is through this mechanism that the enzyme converts anthocyanidins to anthocyanins as a part of the phenylpropanoid pathway. One specific example would be this enzymes actions on pelargonidin. Flavonol 3-O-glucosyltransferase binds the glucoside to this protein, making pelargonidin 3-O-glucoside. This enzyme is also involved in the flavone glycoside pathway, and daphnetin modification in some organisms. The role of the enzyme in these pathways is, again, to bind a glucoside to the substrate to construct a flavonol 3-O-glucoside.^[6]

This enzyme belongs to the family of glycosyltransferases, specifically the hexosyltransferases. The systematic name of this enzyme class is UDP-glucose:flavonol 3-O-D-glucosyltransferase. Other names in common use include:

• GTI,
• uridine diphosphoglucose-flavonol 3-O-glucosyltransferase,
• UDP-glucose:flavonol 3-O-glucosyltransferase, and
• UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT).

Among those, UFGT is divided into UDP-glucose: Flavonoid 3-O-glucosyltransferase (UF3GT) and UDP-glucose: Flavonoid 5-O-glucosyltransferase (UF5GT), which are responsible for the glucosylation of anthocyanins to produce stable molecules.^[7]

Some of the inhibitors of this enzyme include CaCl₂, CoCl₂, Cu⁺², CuCl₂, KCl, Mg⁺², and Mn⁺².^[8] The primary active site residue of this enzyme is Asp181, as determined by studies of how mutations affect enzyme capacity.^[9] There are several documentations of the crystalline structure of flavonol 3-O-glucosyltransferase (2C1X, 2C1Z, and 2C9Z),^[10] and, based on these renderings of the enzyme, there is only one subunit in the quaternary structure of the molecule.