The key
proteins responsible for
hormone synthesis in the thyroid are glycosylated.
Oligosaccharides strongly affect the function of
glycosylated proteins. Both
thyroid-stimulating hormone (TSH) secreted by the pituitary gland and
TSH receptors on the surface of thyrocytes contain N-
glycans, which are crucial to their proper activity.
Thyroglobulin (Tg), the
protein backbone for synthesis of
thyroid hormones, is a heavily N-
glycosylated protein, containing 20 putative N-glycosylated sites. N-
oligosaccharides play a role in Tg transport into the follicular lumen, where
thyroid hormones are produced, and into thyrocytes, where hyposialylated Tg is degraded. N-
glycans of the cell membrane transporters
sodium/iodide symporter and pendrin are necessary for
iodide transport. Some changes in glycosylation result in abnormal activity of the thyroid and alteration of the metabolic clearance rate of
hormones. Alteration of
glycan structures is a pathological process related to the progression of
chronic diseases such as
thyroid cancers and autoimmunity. Thyroid
carcinogenesis is accompanied by changes in sialylation and fucosylation, β1,6-branching of
glycans, the content and structure of poly-LacNAc chains, as well as O-GlcNAcylation, while in thyroid autoimmunity the main processes affected are sialylation and fucosylation. The glycobiology of the thyroid gland is an intensively studied field of research, providing new data helpful in understanding the role of the
sugar component in thyroid
protein biology and disorders.