Mechanisms and regulation of TSH glycosylation.

Thyroid-stimulating hormone provides an interesting model to study the glycosylation and carbohydrate processing of a heterodimeric glycoprotein with a clear physiological function. The carbohydrate moiety on TSH is required for subunit combination, protection from intracellular proteolysis and aggregation, and for attainment of full biological activity. Recent work, summarized herein, has studied mechanisms and kinetics of TSH carbohydrate maturation and has contrasted processing rates and composition of free and combined subunits. Neuroendocrine factors, such as thyrotropin-releasing hormone, appear to modulate the carbohydrate structure of secreted TSH, which results in a change in the relative bioactivity of the circulating hormone. The biochemical mechanisms by which these carbohydrate alterations occur and how they affect hormone-receptor interaction are currently under investigation.