Crystal structure of GlcAT-S, a human glucuronyltransferase, involved in the biosynthesis of the HNK-1 carbohydrate epitope.
The HNK-1 carbohydrate epitope is found in various neural cell adhesion molecules. Two glucuronyltransferases (GlcAT-P and GlcAT-S) are involved in the biosynthesis of HNK-1 carbohydrate. Our previous study on the crystal structure of GlcAT-P revealed the reaction and substrate recognition mechanisms of this enzyme. Comparative analyses of the enzymatic activities of GlcAT-S and GlcAT-P showed that there are notable differences in the acceptor substrate specificities of these enzymes. To elucidate differences between their specificities, we now solved the crystal structure of GlcAT-S. Residues interacting with UDP molecule, which is a part of the donor substrate, are highly conserved between GlcAT-P and GlcAT-S. On the other hand, there are some differences between these proteins in the manner they recognize their respective acceptor substrates. Phe245, one of the most important GlcAT-P residues for the recognition of acceptors, is a tryptophan in GlcAT-S. In addition, Val320, which is located on the C-terminal long loop of the neighboring molecule in the dimer and critical in the recognition of the acceptor sugar molecule by the GlcAT-P dimer, is an alanine in GlcAT-S. These differences play key roles in establishing the distinct specificity for the acceptor substrate by GlcAT-S, which is further supported by site-directed mutagenesis of GlcAT-S and a computer-aided model building of GlcAT-S/substrate complexes.
Shiba
Tomoo
T
Structural Biology Research Center, Photon Factory, Institute of Materials Structure Science,High Energy Acceleration Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan.
Kakuda
Shinako
S
Ishiguro
Masaji
M
Morita
Ippei
I
Oka
Shogo
S
Kawasaki
Toshisuke
T
Wakatsuki
Soichi
S
Kato
Ryuichi
R
D000595:Amino Acid Sequence; D001665:Binding Sites; D018959:CD57 Antigens / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D000939:Epitopes / Q000235:genetics / Q000276:immunology*; D014453:Glucuronosyltransferase / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis / Q000235:genetics*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D040681:Structural Homology, Protein; D013379:Substrate Specificity
D018959:CD57 Antigens; D000939:Epitopes; C475472:B3GAT2 protein, human; D014453:Glucuronosyltransferase