alpha-1,3-galactosyltransferase 2; isoglobotriaosylceramide synthase; iGb3 synthase; iGb3S (A3GALT2, A3GALT2P, IGBS3S)

Function

• synthesizes galactose-alpha(1,3)-galactose group on the glycosphingolipid isoglobotrihexosylceramide or isogloboside 3 (iGb3) by catalyzing transfer of galactose from UDP-galactose to its acceptor molecule gal-beta-1,4-Glc-ceramide
• can also catalyze the addition of galactose to iGb3 itself to form polygalactose structures

UDP-alpha-D-galactose +

beta-D-galactosyl-(1->4)-beta-N-acetyl-D-glucosaminyl-R

=

UDP +

alpha-D-galactosyl-(1->3)-beta-D-galactosyl-(1->4)-beta-N-acetylglucosaminyl-R

Cofactor: Mn+2

Structure

• conserved DXD motif is involved in cofactor binding
• the Mn+2 interacts with the beta-phosphate group of UDP & may also have a role in catalysis (putative)
• belongs to the glycosyltransferase 6 family

Compartment

G

• Golgi apparatus, Golgi stack membrane
  • also found in numerous large vesicles throughout the cytoplasm of the soma
• single-pass type II membrane protein

Expression

• expressed in thymus & monocyte derived dendritic cells

Notes

• the spliced A3GALT2 mRNA may not be detected in human tissues
• functional activity of human A3GALT2 tested by expressing a chimeric protein containing the catalytic domain of human A3GALT2 is unable to synthesize isogloboside 3 (iGb3)
• in rat, mutant 'Asn-253' of human A3GALT2 completely eliminates alpha-1,3-galactosyltransferase activity

More general terms

• galactosyltransferase
• glycoprotein
• membrane protein

Database

• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=127550
• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:127550
• UniProt: http://www.uniprot.org/uniprot/U3KPV4.html