3,4-Linked fucosyl residues

Lacto-N-fucopentaose II also contains an a-L-fucosyl residue linked to a lacto-iV-tetraose molecule, but in this case it is linked to C4 of the 2-acet-amido-2-deoxy-D-glucose unit. The sequence and linkages were again established by hydrolysis of the permethylated saccharide alcohol.279... 

The consitution of the hexasaccharide lacto-A7-difucohexaose has not yet been fully elucidated, but it appears to have the structure of lacto-iV-fuco-pentaose I, together with an extra L-fucosyl residue, probably linked as in lacto-AT-fucopentaose II.253... 

Lacto- N-difucohexaose (7% of the total oligosaccharides) has not yet been fully characterized, but it appears to be a di-O-fucosyl derivative of lacto-Af -tetraose in which the a-L-fucosyl residues are linked to C-2 of the terminal n-galactose residue (as in lacto-AT-fucopentaose I) and to C-4 of the 2-acetamido-2-deoxy-D-glucose residue (as in lacto-iV-fucopentaose II). ... 

Other reports of fucosylation have suggested the existence of proteins that contain fucose residues attached directly to a serine or threonine. This linkage was first described by the presence of amino acid fucosides in human urine [121] then as components of rat tissue extracts [122] and rat glycoproteins [123]. Release of the glycans by alkaline 3-elimination revealed the presence of both fucitol and Glc(31-3)fucitol [123]. Further examination of these fucosylated glycoproteins in soluble and membrane fractions from rat cells suggests the existence of both cytosolic and membrane associated O-linked fucosylated proteins [124], but the purity of the cytosolic fractions was never examined. 

XylMan3GlcNAc2) also non-xylosylated and a-l,6-fucosylated core structures occur. It has to be mentioned that in plant glycoproteins the frequently found xylosylated trimannosyl-A,A -diacetylchitobiosyl core structure can occur with a 1,3-linked in stead of a 1,6-linked oFuc residue, attached at the asparagine-bound GlcNAc unit (for a review, see ref [38]). 

A fundamental finding revealed that the high affinity binding of N-linked glycopeptides to the pea (and lentil) lectins requires the presence of an a-L-fucosyl residue attached to the asparagine-linked A-acetylglucosamine residue [90,95]. 

The mass shift of the major N-glycan structure in wild-type to the complex-type GnGnXF to the major structure GnGn [lacking the plant-specific 1,3-linked fucosyl (F) and 1,2-linked xylosyl (X) residues] in the glycoengineered transgenic plant is marked by an arrow. 

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