Physiological relevance of protein glycosylation

The glycosylation of proteins is a complex biological pathway which is ordered and non-random. It is also a deterministic pathway dependent upon protein sequence, cellular phenotype, and the physiological environment. Two principal physiological roles have emerged within the past decade for protein-linked glycans: as recognition determinants and as modulators of various protein attributes such as bioactivity, pharmacokinetics, folding, and immunogenicity. All these attributes are crucial to development and application of protein-based pharmaceuticals. However, protein glycosylation represents a difficult structure/function problem since most glycoproteins exhibit microheterogeneity and oligosaccharides frequently contribute to this heterogeneity. Nevertheless, recent data suggest that different members of the heterogeneous ensemble exhibit distinguishable intrinsic properties, suggesting that the microheterogeneity of protein glycosylation represents a sophisticated mechanism of biological control.