The acceptor substrate specificity of human beta4-galactosyltransferase V indicates its potential function in O-glycosylation.
In order to assess the function of the different human UDP-Gal:GlcNAc beta4-galactosyltransferases, the cDNAs of two of them, beta4-GalT I and beta4-GalT V, were expressed in the baculovirus/insect cell expression system. The soluble recombinant enzymes produced were purified from the medium and used to determine their in vitro substrate specificities. The specific activity of the recombinant beta4-GalT V was more than 15 times lower than that of beta4-GalT I, using GlcNAc beta-S-pNP as an acceptor. Whereas beta4-GalT I efficiently acts on all substrates having a terminal beta-linked GlcNAc, beta4-GalT V appeared to be far more restricted in acceptor usage. Beta4-GalT V acts with high preference on acceptors that contain the GlcNAc beta1-->6GalNAc structural element, as found in O-linked core 2-, 4- and 6-based glycans, but not on substrates related to V-linked or blood group I-active oligosaccharides. These results suggest that beta4-GalT V may function in the synthesis of lacNAc units on O-linked chains, particularly in tissues which do not express beta4-GalT I, such as brain.
van Die
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I
Department of Medical Chemistry, Vrije Universiteit, Amsterdam, The Netherlands. im.van_die.medchem@med.vu.nl
van Tetering
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A
Schiphorst
W E
WE
Sato
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T
Furukawa
K
K
van den Eijnden
D H
DH
D016367:Baculoviridae / Q000235:genetics; D015153:Blotting, Western; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D018076:DNA, Complementary / Q000378:metabolism; D005700:Galactosyltransferases / Q000235:genetics / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D007700:Kinetics; D007768:Lactalbumin / Q000378:metabolism; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
D018076:DNA, Complementary; D011994:Recombinant Proteins; D007768:Lactalbumin; D005700:Galactosyltransferases