FIGURE 5.8. Catalytic site of bovine β1–4 galactosyltransferase.


Catalytic site of bovine β1–4 galactosyltransferase. Composite figure shows selected residues/atoms of the superimposition of the donor complex (PDB ID 1tw1) on the acceptor complex (PDB ID 1tw5). O4 designates the C4 hydroxyl group of the GlcNAcβ1–4GlcNAc acceptor substrate positioned for in-line SN2 attack (arrow) on C1 of the UDP-Gal donor substrate. The base form of D318 serves to partially deprotonate the C4 hydroxyl group rendering it a better nucleophile. The positively charged Mg++ ion coordinates the two phosphates of the UDP leaving group, promoting cleavage of the C1-Pβ bond by stabilizing the additional negative charge that develops on Pβ of the leaving group. D252-V253-D254 corresponds to the DXD motif in bovine β1–4 galactosyltransferase.

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From: Chapter 5, Glycosyltransferases and Glycan-processing Enzymes

Cover of Essentials of Glycobiology
Essentials of Glycobiology. 2nd edition.
Varki A, Cummings RD, Esko JD, et al., editors.
Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 2009.
Copyright © 2009, The Consortium of Glycobiology Editors, La Jolla, California.

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