| Structural highlights
Function
B4GT7_DROME Transfers galactose from UDP-D-Galactose (UDP-Gal) to the acceptor xylose residue in the linkage tetrasaccharide region of the glycosaminoglycan side chain of proteoglycans (PubMed:12215432, PubMed:12244071, PubMed:12590131, PubMed:20236943). No activity towards beta-GlcNAc, beta-Glc, beta-Gal, and beta-GalNAc as acceptors (PubMed:12244071, PubMed:12590131).[1] [2] [3] [4]
Publication Abstract from PubMed
The beta-1,4-galactosyltransferase 7 (beta4GalT7) enzyme is involved in proteoglycan synthesis. In the presence of a manganese ion, it transfers galactose from UDP-galactose to xylose on a proteoglycan acceptor substrate. We present here the crystal structures of human beta4GalT7 in open and closed conformations. A comparison of these crystal structures shows that, upon manganese and UDP or UDP-Gal binding, the enzyme undergoes conformational changes involving a small and a long loop. We also present the crystal structures of Drosophila wild-type beta4GalT7 and D211N beta4GalT7 mutant enzymes in the closed conformation in the presence of the acceptor substrate xylobiose and the donor substrate UDP-Gal, respectively. To understand the catalytic mechanism, we have crystallized the ternary complex of D211N beta4GalT7 mutant enzyme in the presence of manganese with the donor and the acceptor substrates together in the same crystal structure. The galactose moiety of the bound UDP-Gal molecule forms seven hydrogen bonds with the protein molecule. The nonreducing end of the xylose moiety of xylobiose binds to the hydrophobic acceptor sugar binding pocket created by the conformational changes, whereas its extended xylose moiety forms hydrophobic interactions with a Tyr residue. In the ternary complex crystal structure, the nucleophile O4 oxygen atom of the xylose molecule is found in close proximity to the C1 and O5 atoms of the galactose moiety. This is the first time that a Michaelis complex of a glycosyltransferase has been described, and it clearly suggests an SN2 type catalytic mechanism for the beta4GalT7 enzyme.
Crystal Structures of beta-1,4-Galactosyltransferase 7 Enzyme Reveal Conformational Changes and Substrate Binding.,Tsutsui Y, Ramakrishnan B, Qasba PK J Biol Chem. 2013 Nov 1;288(44):31963-70. doi: 10.1074/jbc.M113.509984. Epub 2013, Sep 19. PMID:24052259[5]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Nakamura Y, Haines N, Chen J, Okajima T, Furukawa K, Urano T, Stanley P, Irvine KD, Furukawa K. Identification of a Drosophila gene encoding xylosylprotein beta4-galactosyltransferase that is essential for the synthesis of glycosaminoglycans and for morphogenesis. J Biol Chem. 2002 Nov 29;277(48):46280-8. PMID:12215432 doi:10.1074/jbc.M203873200
- ↑ Vadaie N, Hulinsky RS, Jarvis DL. Identification and characterization of a Drosophila melanogaster ortholog of human beta1,4-galactosyltransferase VII. Glycobiology. 2002 Oct;12(10):589-97. PMID:12244071 doi:10.1093/glycob/cwf074
- ↑ Takemae H, Ueda R, Okubo R, Nakato H, Izumi S, Saigo K, Nishihara S. Proteoglycan UDP-galactose:beta-xylose beta 1,4-galactosyltransferase I is essential for viability in Drosophila melanogaster. J Biol Chem. 2003 May 2;278(18):15571-8. PMID:12590131 doi:10.1074/jbc.M301123200
- ↑ Ramakrishnan B, Qasba PK. Crystal structure of the catalytic domain of Drosophila beta1,4-Galactosyltransferase-7. J Biol Chem. 2010 May 14;285(20):15619-26. Epub 2010 Mar 17. PMID:20236943 doi:10.1074/jbc.M109.099564
- ↑ Tsutsui Y, Ramakrishnan B, Qasba PK. Crystal Structures of beta-1,4-Galactosyltransferase 7 Enzyme Reveal Conformational Changes and Substrate Binding. J Biol Chem. 2013 Nov 1;288(44):31963-70. doi: 10.1074/jbc.M113.509984. Epub 2013, Sep 19. PMID:24052259 doi:http://dx.doi.org/10.1074/jbc.M113.509984
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