Carbohydrate and hydrophobic-carbohydrate recognition sites (CARS and HY-CARS) in solubilized glycosyltransferases.
Six different glycosyltransferases that are active with glycosphingolipid substrates have been purified from Golgi-membranes after solubilization with detergents. It appears that GalT-4(UDP-Gal:GlcNAc-R1 beta 1-4GalT), GalNAcT-2(UDP-Gal:Gal alpha-R2 beta 1-3GalNAcT) and FucT-2(GDP-Fuc:Gal beta GlcNAc-R3 alpha 1-2FucT) are specific for oligosaccharides bound to ceramide or to a protein moiety. These are called CARS (carbohydrate recognition sites) glycosyltransferases (GLTs). On the other hand, GalT-3(UDP-Gal:GM2 beta 1-3GalT), GalNAcT-1(UDP-GalNAc:GM3 beta 1-4GalNAcT) and FucT-3 (GDP-Fuc:LM1 alpha 1-3FucT) recognize both hydrophobic moieties (fatty acid of ceramide) as well as the oligosaccharide chains of the substrates. These GLTs are called HY-CARS (hydrophobic and carbohydrate recognition sites). D-Erythro-sphingosine (100-500 microM) modulates the in vitro activities of these GLTs. Modulation depends on the binding of D-sphingosine to a protein backbone, perhaps on more than one site and beyond transmembrane hydrophobic domains. Control of GLTs by free D-sphingosine was suggested with the concomitant discovery of ceramide glycanase in rabbit mammary tissues. The role of free sphingosine as an in vivo homotropic modulator of glycosyltransferases is becoming apparent.
Basu
S
S
Department of Chemistry and Biochemistry, University of Notre Dame, IN 46556.
Ghosh
S
S
Basu
M
M
Hawes
J W
JW
Das
K K
KK
Zhang
B J
BJ
Li
Z X
ZX
Weng
S A
SA
Westervelt
C
C
D000818:Animals; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000737:chemistry; D002417:Cattle; D002518:Ceramides / Q000737:chemistry / Q000378:metabolism; D003902:Detergents; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism; D005700:Galactosyltransferases / Q000378:metabolism*; D006056:Golgi Apparatus / Q000201:enzymology*; D006168:Guinea Pigs; D006602:Hexosyltransferases / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D011817:Rabbits; D012995:Solubility; D013110:Sphingosine / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins
D002241:Carbohydrates; D002518:Ceramides; D003902:Detergents; D005227:Fatty Acids; D005700:Galactosyltransferases; D006602:Hexosyltransferases; D013110:Sphingosine; C021451:inulosucrase; D001426:Bacterial Proteins