Glycosyl transferase 25 domain 2 (GLT25D2) is a glucosyltransferase enzyme expressed only at low levels in the nervous system. Glycosyltransferases are enzymes that act as a catalyst for the transfer of a monosaccharide unit from an activated nucleotide sugar (also known as the "glycosyl donor") to a glycosyl acceptor molecule, usually an alcohol. Glycosyl transferases transfer glycosyl groups onto their substrate. Localization partially defines their function. Glt25D2 enzyme showed a strong galactosyltransferase activity toward various types of collagen and toward the serum mannose-binding lectin MBL which contains a collagen domain.