3otk

Publication Abstract from PubMed

Leukocyte-type core 2 beta1,6-N-acetylglucosaminyltransferase (C2GnT-L) is an inverting, metal-ion-independent glycosyltransferase that catalyzes the formation of mucin-type core 2 O-glycans. C2GnT-L belongs to the GT-A fold, yet it lacks the metal ion binding DXD motif characteristic of other nucleoside disphosphate GT-A fold glycosyltransferases. To shed light on the basis for its metal ion independence, we have solved the X-ray crystal structure (2.3 A resolution) of a mutant form of C2GnT-L (C217S) in complex with the nucleotide sugar product UDP and, using site-directed mutagenesis, examined the roles of R378 and K401 in both substrate binding and catalysis. The structure shows that C2GnT-L exists in an "open" conformation and a "closed" conformation and that, in the latter, R378 and K401 interact with the beta-phosphate moiety of the bound UDP. The two conformations are likely to be important in catalysis, but the conformational changes that lead to their interconversion do not resemble the nucleotide-sugar-mediated loop ordering observed in other GT-A glycosyltransferases. R378 and K401 were found to be important in substrate binding and/or catalysis, an observation consistent with the suggestion that they serve the same role played by metal ion in all of the other GT-A glycosyltransferases studied to date. Notably, R378 and K401 appear to function in a manner similar to that of the arginine and lysine residues contained in the RX(4-5)K motif found in the retaining GT-B glycosyltransferases.

Structural and mechanistic characterization of leukocyte-type core 2 beta1,6-N-acetylglucosaminyltransferase: a metal-ion-independent GT-A glycosyltransferase.,Pak JE, Satkunarajah M, Seetharaman J, Rini JM J Mol Biol. 2011 Dec 16;414(5):798-811. Epub 2011 Oct 26. PMID:22056345^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.