Trimannosyl chitobiose

Fig. 15.1. The A/-glycan biosynthetic pathway, illustrating how the three classes of A/-glycans (high mannose, hybrid and complex glycans) are derived from a common biosynthetic precursor. The trimannosyl-chitobiose core, which is common to all A/-glycans, is outlined on the precursor A/-glycan. Glc, o Man, GIcNAc.

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. 

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