Characterization of glycoproteins: carbohydrate structures of glycoprotein hormones.

Abstract

Gylcoproteins are a complex group of macromolecules that are widely distributed in nature. They are present virtually in all forms of life and are involved in important biological functions (Wagh and Bahl, 1981; Sharon and Liz, 1982; Kobata, 1984). The importance of the role that the carbohydrates play in the functions of glycoproteins has been fairly well recognized (Ashwell and Harford, 1982; Kalyan et al., 1982; Kalyan and Bahl, 1983). In recent years, considerable progress has been made toward our understanding of the structure, function, and biosynthesis of the carbohydrates (Kornfeld and Kornfeld, 1985). This has been due largely to the refinement in oligosaccharide separation and structural techniques. A vast amount of structural information gathered as a result has revealed that microheterogeneity is of general occurrence in glycoproteins. The function of this microheterogeneity is ambiguous at present. Moreover, it is difficult to reconcile the phenomenon of microheterogeneity with the fact that there is an intimate and precise relationship between structure and function in biological macromolecules. Nevertheless, the existence of microheterogeneity has complicated the structural determination of the carbohydrate prosthetic groups. In the seventies, microheterogeneity was merely considered as an artifact and was ignored during the structural determination of heterosaccharides. Consequently, the structures reported then were average structures and should be reexamined (Kobata, 1984). In this report, the problem of micro-heterogeneity the general strategy for heterosaccharide structural characterization are considered with respect to three glycoprotein hormones: human choriogonadotropin (hCG), ovine luteinizing hormone (oLH), and equine choriogonadotropin (eCG).