Secretion of sulfated thyroglobulin.

Area of Science:

• Cell Biology
• Biochemistry
• Endocrinology

Background:

• Thyroid follicle cells synthesize and secrete thyroglobulin.
• Sulfate incorporation into proteins is a key post-translational modification.

Purpose of the Study:

• To identify the site of sulfate incorporation in thyroid cells.
• To determine which components of thyroglobulin are sulfated.
• To investigate the role of sulfate residues in thyroglobulin function.

Main Methods:

• Autoradiography (light and electron microscopy) to visualize sulfate incorporation.
• Incubation of isolated thyroid follicles with radioactive sulfate.
• Polyacrylamide gel electrophoresis to analyze secreted products.
• Enzymatic digestion (endoglycosidase H, endoglycosidase D) and acid hydrolysis to characterize sulfate attachment.

Main Results:

• Sulfate is primarily incorporated in the Golgi complex.
• Secreted thyroglobulin is sulfated, with approximately 13 sulfate residues per dimeric molecule.
• Sulfate residues are attached to high-mannose carbohydrate side chains and tyrosine.
• Sulfate contributes to thyroglobulin's anionic nature and is accessible to sulfatases.

Conclusions:

• Thyroglobulin is a sulfated glycoprotein.
• Sulfate residues on thyroglobulin may regulate intracellular transport and lumenal packaging.
• Tyrosine sulfation and O-linked glycosylation-associated sulfation occur on thyroglobulin.