| First Author | Kouno T | Year | 2011 |
| Journal | J Biol Chem | Volume | 286 |
| Issue | 36 | Pages | 31337-46 |
| PubMed ID | 21771787 | Mgi Jnum | J:324260 |
| Mgi Id | MGI:7278687 | Doi | 10.1074/jbc.M111.233353 |
| Citation | Kouno T, et al. (2011) Specific enzyme complex of beta-1,4-galactosyltransferase-II and glucuronyltransferase-P facilitates biosynthesis of N-linked human natural killer-1 (HNK-1) carbohydrate. J Biol Chem 286(36):31337-46 |
| abstractText | Human natural killer-1 (HNK-1) carbohydrate is highly expressed in the nervous system and is involved in synaptic plasticity and dendritic spine maturation. This unique carbohydrate, consisting of a sulfated trisaccharide (HSO(3)-3GlcAbeta1-3Galbeta1-4GlcNAc-), is biosynthesized by the successive actions of beta-1,4-galactosyltransferase (beta4GalT), glucuronyltransferase (GlcAT-P and GlcAT-S), and sulfotransferase (HNK-1ST). A previous study showed that mice lacking beta4GalT-II, one of seven beta4GalTs, exhibited a dramatic loss of HNK-1 expression in the brain, although beta4GalT-I-deficient mice did not. Here, we investigated the underlying molecular mechanism of the regulation of HNK-1 expression. First, focusing on a major HNK-1 carrier, neural cell adhesion molecule, we found that reduced expression of an N-linked HNK-1 carbohydrate caused by a deficiency of beta4GalT-II is not likely due to a general loss of the beta1,4-galactose residue as an acceptor for GlcAT-P. Instead, we demonstrated by co-immunoprecipitation and endoplasmic reticulum-retention analyses using Neuro2a (N2a) cells that beta4GalT-II physically and specifically associates with GlcAT-P. In addition, we revealed by pulldown assay that Golgi luminal domains of beta4GalT-II and GlcAT-P are sufficient for the complex to form. With an in vitro assay system, we produced the evidence that the kinetic efficiency k(cat)/K(m) of GlcAT-P in the presence of beta4GalT-II was increased about 2.5-fold compared with that in the absence of beta4GalT-II. Finally, we showed that co-expression of beta4GalT-II and GlcAT-P increased HNK-1 expression on various glycoproteins in N2a cells, including neural cell adhesion molecule. These results indicate that the specific enzyme complex of beta4GalT-II with GlcAT-P plays an important role in the biosynthesis of HNK-1 carbohydrate. |
