[The inherent fluorescence of thyroglobulin]

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• Thyroglobulin is a key protein in thyroid hormone synthesis.
• Alterations in thyroglobulin structure may be associated with thyroid pathologies like goiter.
• Understanding protein conformation is crucial for comprehending biological function.

Purpose of the Study:

• To investigate the fluorescence properties of tryptophan and tyrosine in normal and goiter human thyroglobulin.
• To examine the effects of iodination on thyroglobulin structure.
• To analyze conformational changes in bovine thyroglobulin under varying pH conditions.

Main Methods:

• Fluorescence spectroscopy was used to study tryptophan and tyrosine residues.
• Intact and iodinated thyroglobulin samples from normal and pathological thyroids were analyzed.
• Bovine thyroglobulin was subjected to different pH levels to observe denaturation and conformational shifts.

Main Results:

• In normal thyroglobulin, 95% of tryptophan residues are buried within the globule.
• In pathological (goiter) thyroglobulin, only 68% of tryptophan residues are inaccessible to water.
• Iodination induced a redistribution of tryptophan residues in pathological thyroglobulin.
• Bovine thyroglobulin showed spectral shifts and decreased quantum yield at extreme pH, indicative of denaturation.
• A conformational transition in bovine thyroglobulin occurred between pH 6-7, affecting energy transfer to iodoamino acids.

Conclusions:

• Significant differences in tryptophan residue accessibility exist between normal and goiter human thyroglobulin.
• Iodination impacts the structural organization of tryptophan in pathological thyroglobulin.
• Thyroglobulin undergoes pH-dependent conformational changes and denaturation, influencing its functional properties.