Characterization of T(4)-binding globulin cleaved by human leukocyte elastase

Area of Science:

• Biochemistry
• Endocrinology
• Molecular Biology

Background:

• Thyroxine-binding globulin (TBG) is crucial for maintaining serum thyroid hormone levels and preventing urinary loss.
• TBG's role in hormone distribution and delivery to tissues is not fully understood.
• TBG, a serpin superfamily member, is noninhibitory despite sequence homology to serine proteinase inhibitors.

Purpose of the Study:

• To investigate the effects of elastase cleavage on TBG's structure and function.
• To clarify the mechanism of TBG's involvement in thyroid hormone tissue delivery.
• To reconcile conflicting reports on elastase-cleaved TBG's hormone-binding properties.

Main Methods:

• Confirmation of TBG cleavage by elastase and associated conformational changes.
• Assessment of the T(4)-binding affinity of cleaved TBG.
• Evaluation of heat stability changes in cleaved TBG.
• Analysis of further fragmentation and its impact on the hormone-binding site.

Main Results:

• Elastase cleavage of TBG was confirmed, inducing characteristic conformational changes.
• Contrary to previous findings, cleaved TBG exhibited reduced T(4)-binding affinity.
• Cleaved TBG showed increased heat stability.
• Further fragmentation led to loss of the hormone-binding site, consistent with in vivo observations.

Conclusions:

• Elastase cleavage significantly alters TBG's T(4)-binding affinity and stability.
• TBG's interaction with proteinases suggests a role in targeted thyroid hormone delivery to specific tissues.
• These findings provide insights into the dynamic function of TBG in hormone transport and tissue targeting.