thyroglobuline

Thyroglobulin is a large glycoprotein synthesized by thyroid follicular cells and stored in the colloid of thyroid follicles. It serves as the substrate and reservoir for thyroid hormone synthesis. Thyroglobulin is a dimeric protein rich in tyrosine residues, with multiple sites that can be iodinated to form thyroid hormones.

During hormone production, thyroglobulin is secreted into the follicular lumen and iodinated by thyroid peroxidase to form monoiodotyrosine and diiodotyrosine residues. Coupling of iodinated tyrosines within the thyroglobulin molecule generates the hormones T3 and T4, which remain attached to the protein until needed. Thyroglobulin therefore stores iodinated hormone precursors in the colloid until stimulation by thyroid-stimulating hormone (TSH).

When thyroid activity requires hormones, colloid containing iodinated thyroglobulin is endocytosed by follicular cells, degraded by lysosomal proteolysis, and free T3 and T4 are released into the bloodstream. Small amounts of thyroglobulin and its fragments may also enter circulation.

Clinical relevance: Serum thyroglobulin is used as a tumor marker for differentiated thyroid cancer after thyroidectomy and radioactive iodine therapy; rising levels can suggest recurrence. Interpretation is affected by anti-thyroglobulin antibodies, which can interfere immunoassays and obscure results.

Genetics and pathology: The TG gene encodes thyroglobulin and is expressed in the thyroid. Mutations can cause congenital hypothyroidism and goiter. Autoimmune thyroid diseases may feature anti-thyroglobulin antibodies.