GCNT2

GCNT2 encodes β1-6-N-acetylglucosaminyltransferase (IGnT), which synthesizes β1-6 branched N-acetylglucosamine on the N-acetyllactosamine structure (mainly poly-N-acetyllactosamine structure). Linear poly-N-acetyllactosamine structure often seen in fetal erythrocyte surface is known as the i antigen of the I/i blood type antigens, and the branched poly-N-acetyllactosamine structure is present in adult humans as the I antigen, which is synthesized by GCNT2 (known as I enzyme, I-branching enzyme, GCNT2, IGnT). This enzyme shows 3 variant sequences [IGnTA(IGnT1), IGnTB(IGnT2), IGnT(IGnT3)], and the different isoforms have respective roles in tissue expressions. The genome sequence has 3 first exons consisted of the promotor domain and ORF, followed by exon 2 and 3 commonly used (catalytic domains are encoded on exon 2 and 3). IGnTC is reported to be related in expression of the Ii blood type antigen. IGnTB or all the isoforms are considered as a causative gene of congenital cataract. Basic substrate specificity is similar among the isoforms but some differences are known. For instance, IGnTA and IGnTB are similar but IGnTB has lower activity to NeuAca2-6Galb1-4GlcNAcb1-3Galb1-4Glc than IGnTA does, but shows higher activity to Gala1-3Galb1-4GlcNAcb1-3Galb1-4Glc.