X-glycans

The core structure of X-glycans is invariably the trimannosyl chitobiose unit, Man3GlcNAc2, which can be a6-fucosylated at the reducing end GlcNAc. In plants, this core fiicosylation is a3 where it occurs, with and without additional / 2-xylosylation at the /3-mannose. In insects, either or both types of core fiicosylation can occur but not /32-xylosylation, whereas in some other lower animals that have been looked at, including mollusks and nematodes, instances of all these core modifications could be found. 

Wang W, Hu T, Frantom PA, Zheng T, Gerwe B, Del Amo DS, Garret S, Seidel RD HI, Wu P (2009) Chemoenzymatic synthesis of GDP-L-fucose and the Lewis X glycan derivatives. Proc Natl Acad Sci USA 106 16096-16101... 

Maras, M., Saelens, X., Laroy, W. et al. (1997) In vitro conversion of the carbohydrate moiety of fungal glycoproteins to mammalian-type oligosaccharides - evidence for JV-acetylglucosaminyltransferase-I-accepting glycans from Trichoderma reesei. European Journal of Biochemistry, 249 (3), 701-707. 

Ramirez-Soto, D. and Poretz, R.D. (1991) The (l-3)-linked (X-L-fucosyl group of the IV-glycans of the Wistaria floribunda lectins is recognised by a rabbit antiserum. Carbohydate Research 213, 27-36. 

T. A. Gerken, Kinetic modeling confirms the biosynthesis of mucin core 1 (/i-Gal (1 -3)x-Gal YAc-O-Ser/Thr) O-glycan structures are modulated by neighboring glycosylation effects, Biochemistry, 43 (2004) 4137—4142. 

Purification of the conjugates may be done by reverse phase HPLC separation. Dry the reaction solution under a nitrogen stream and reconstitute in a minimum volume of acetonitrile/water (1 1, v/v). Apply the sample to a 5 pm Cig-silica HPLC column (250 X 4.6 mm, Nucleosil). Elute with a gradient of water to acetonitrile at a flow rate of 1 ml/minute over a time course of 30 minutes. Free BNAH and BNAH-glycan derivatives can be monitored by absorbance at 275 nm. The conjugate peak also will be positive for carbohydrate by reaction with orcinol, which can be detected by spray after spotting a small eluted sample on a TLC plate. 

Chen, M., Liu, X., Wang, Z., Qi, Q., and Wang, P.G. 2005. Modification of plant V-glycan processing the future of producing therapeutic protein by transgenic plants. Medical Research Reviews 25(3), 343-360. 

Morrow, A. L., Ruiz-Palados, G. M., Jiang, X., and Newburg, D. S. (2005). Human-milk glycans that inhibit pathogen binding protect breast-feeding infants against infectious diarrhea. /. Nutr. 135,1304—1307. 

In view of the efficient inhibition of a particular crystalline glycan hydrolase by the epoxylbutyl -cellobioside 7 (n = 2), we decided to prepare the deoxy iodo derivative 21 to aid in the X-ray crystallographic analysis. We soon found that, although the alkene 22 was easily available as a direct precursor to our target, the epoxide functionality had to be introduced indirectly using bromo-hydrin 23 technology any direct oxidation of 22 invariably led to some loss of the iodine atom [23]. 

Fig. 21.—Proposed Structures of Glycopeptides 1 and 2 of Glycan of Human Chorionic Gonadotropin a-Subunit (X = Unknown Substituent).121...

The first, X-ray diffraction results obtained favor the T conformation. In collaboration with the Laboratory of the Physics of Solids at the University of Lille, we have undertaken an initial series of experiments that concern the structures of oligosaccharides of low molecular weight that exist in complete glycans, as prepared from glycoprotein-osis urines or by chemical and enzymic splitting of different glycans. 

The conformation of some glycans has been studied with the aid of molecular models. For structures of the N-acetyl-lactosaminic type, having two antennae, two conformations are possible, the Y and the T. Results from X-ray diffraction studies favor the T conformation. Both conformations are in good agreement with the role of recognition signal that the glycans could play. 

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