HNK-1抗原の生合成に関与するグルクロン酸転移酵素とその機能に関する研究

点击翻译按钮获取中文摘要

In our previous studies, we succeeded in cloning of two kind of glucuronyltransferase (GlcAT-P and GlcAT-S) cDNAs that are responsible for the biosynthesis of the HNK-1 epitope and studied the functions of the HNK-1 epitope using these cDNAs as molecular probes. In this study, we have cloned the human GlcAT-P gene for the first time and revealed that the en-zyme is a type II membrane protein consisting of 334 amino acids and the amino acid se-quence of the catalytic region is 98.2% identical to that of rat GlcAT-P but is different from the latter in the 13 amino acid shorter C-terminal cytoplasmic domain. The human GlcAT-P gene was mapped to 11q25, which is syntenic with the mouse GlcAT-P locus, the A4 region of chromosome 9. The acceptor specificity of a rat brain glucuronyltransferase, GlcAT-P,was investigated using asialoorosomucoid as a model acceptor substrate. The enzyme trans-ferred glucuronic acid to bi-, tri-, and tetra-antennary complex type sugar chains, with almost equal efficiency, indicating that the enzyme has no preference as to the number of acceptor sugar branches. The GlcAT-P is highly specific for the terminal W-acetyllactosamine structure and no glucuronic acid was incorporated into a Galbl-3GlcNAc branch. The GlcAT-P transferred glucuronic acid to the galactose residues in each N-acetyllactosamine residue of the tetra-antennary oligosaccharide chains with different efficiencies and most preferentially to those in the Galbl-4GlcNAcbl-4Manal-3 branch. With regards to the membrane phospholipid requirement of GlcAT-P, we demonstrated that phosphatidyl inositol is required for the GlcAT-P activity to glycolipid substrate, paragloboside.