Cellular folding pathway of a metastable serpin

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Folding

Background:

• Some proteins exist in metastable states, enabling them to perform physiological work through conformational changes.
• The serpin family, including antithrombin III (ATIII), are metastable protease inhibitors that undergo significant conformational changes.
• Misfolding of ATIII, a key inhibitor in blood coagulation, is linked to thrombosis and other diseases.

Purpose of the Study:

• To investigate the in-cell folding pathway of antithrombin III (ATIII).
• To understand how ATIII achieves its active, metastable conformation and avoids more stable, inactive states.
• To elucidate the role of disulfide bond formation order in ATIII folding and function.

Main Methods:

• Studied the in-cell folding of antithrombin III (ATIII).
• Analyzed the order of disulfide bond formation.
• Investigated the influence of N-linked glycans and molecular chaperones on ATIII folding.

Main Results:

• ATIII folding exhibits a biased disulfide bond formation order, with early C-terminal disulfide formation preceding N-terminal disulfides.
• This specific folding order constrains the reactive center loop (RCL), maintaining its accessibility.
• N-linked glycans and chaperones aid in efficient folding and secretion of functional ATIII.
• Disease-associated ATIII variants demonstrate impaired folding, explaining their pathological phenotypes.

Conclusions:

• The biased disulfide bond formation order is critical for ATIII to achieve its active, metastable state.
• Proper folding of ATIII is essential for its function as a protease inhibitor and preventing disease.
• Cellular factors like glycans and chaperones play a significant role in ensuring functional ATIII folding.