Involvement of murine β-1,4-galactosyltransferase V in lactosylceramide biosynthesis

Abstract

Human β-1,4-galactosyltransferase (β-1,4-GalT) V was shown to be involved in the biosynthesis of N-glycans, O-glycans and lactosylceramide (Lac-Cer) by in vitro studies. To determine its substrate specificity, enzymatic activity and its products were analyzed using mouse embryonic fibroblast (MEF) cells from β-1,4-GalT V (B4galt5)-mutant mice. Analysis of expression levels of the β-1,4-GalT I-VI genes revealed that the expression of the β-1,4-GalT V gene in B4galt5+/−- and B4galt5−/−-derived MEF cells are a half and null when compared to that of B4galt5+/+-derived MEF cells without altering the expression levels of other β-1,4-GalT genes. These MEF cells showed no apparent difference in their growth. When β-1,4-GalT activities were determined towards GlcNAcβ-S-pNP, no significant difference in its specific activity was obtained among B4galt5+/+-, B4galt5+/−- and B4galt5−/−-derived MEF cells. No significant differences were obtained in structures and amounts of N-glycans and lectin bindings to membrane glycoproteins among B4galt5+/+-, B4galt5+/−- and B4galt5−/−-derived MEF cells. However, when cell homogenates were incubated with glucosylcer-amide in the presence of UDP-[3H]Gal, Lac-Cer synthase activity in B4galt5+/−- and B4galt5−/−-derived MEF cells decreased to 41% and 11% of that of B4galt5+/+-derived MEF cells. Consistent with this, amounts of Lac-Cer and its derivative GM3 in B4galt5−/−-derived MEF cells decreased remarkably when compared with those of B4galt5+/+ derived MEF cells. These results indicate that murine β-1,4-GalT V is involved in Lac-Cer biosynthesis.

Terminal Galactosylation and Sialylation Switching on Membrane Glycoproteins upon TNF-Alpha-Induced Insulin Resistance in Adipocytes

“…The role of these glycans and glycosyltransferases in the pathophysiology of IR in adipose is unknown, and further experiments are required to pinpoint the exact mechanisms or consequences of the observed changes. It is also interesting to note that B4GalT5 expression has been implicated in the synthesis of lactosylceramide (57), and aberrant ceramide metabolism has a wellestablished role in IR (58).…”

Association of Shiga toxin glycosphingolipid receptors with membrane microdomains of toxin-sensitive lymphoid and myeloid cells

“…This novel fi nding suggests that the expression of ␤ 1,4-GalT6 may not be obligatory for the biosynthesis of Lc2Cer, which represents the start-up compound for the biosynthesis of many GSLs. However, ␤ 1,4-GalT5 can also catalyze the synthesis of Lc2Cer ( 96,97 ) and may compensate for the lack of ␤ 1,4-GalT6 and thus take over the biosynthesis of Lc2Cer in Raji cells. The resulting amounts of Lc2Cer are relatively low in Raji cells, presumably because of the requirement for Lc2Cer as a precursor for the synthesis of Gb3Cer or alternatively for the biosynthesis of ganglioside II 3 Neu5Ac-Lc2Cer (GM3) and GM3-derived ganglio-series gangliosides, such as GM2 and GM1, or higher sialylated gangliosides, like GD3 and GD2 and others.…”

Tight Complex Formation between Cosmc Chaperone and Its Specific Client Non-native T-synthase Leads to Enzyme Activity and Client-driven Dissociation

“…The formation of this class of enzymes in the ER and their movements to other organelles in the secretory pathway may require a suite of chaperones and additional proteins for correct folding/localization/activity, as shown recently for chitin synthase III, which requires Chs7p to prevent oligomerization and allow COPII vesicle export from the ER (50), the Drosophila Golgi ␤4GalNAcTB, which requires GABPI (51), the ER proteins POMT1/POMT2, which are both required for functional O-mannosyltransferase (52), Golgi EXT1/EXT2, which are both required for functional heparin sulfate biosynthesis (53), Golgi ␤4GalT-V and -VI, which require membrane factors to function in transferring Gal from UDP-Gal to Glc (54), and the Golgi GnT1IP, which is an inhibitory protein of GnT1 and is required for expression of high mannose-type N-glycans in testis (55). However, mechanistically little is known about such systems, and it is possible that other glycosyltransferases may need chaperones or co-factors to regulate their activities, but clearly more research is needed.…”