Novel covalent chaperone complexes associated with human chorionic gonadotropin beta subunit folding intermediates

Area of Science:

• Cell Biology
• Protein Biochemistry
• Endocrinology

Background:

• Molecular chaperones are crucial for protein folding within the endoplasmic reticulum (ER).
• The human chorionic gonadotropin beta subunit (hCG-beta) is a secretory protein whose ER folding has been previously studied.
• Stable detection of chaperone complexes with wild-type hCG-beta is challenging due to its rapid folding (t1/2 = 4-5 min).

Purpose of the Study:

• To investigate if chaperone complex detection depends on carbohydrate absence or folding rate.
• To determine if hCG-beta-chaperone complexes lead to mature, secreted hCG-beta.
• To elucidate the nature of the binding between hCG-beta and its chaperones.

Main Methods:

• Analysis of chaperone-containing complexes in hCG-beta folding mutants.
• Comparison of chaperone binding in the presence and absence of N-linked oligosaccharides.
• Characterization of the binding interactions and their role in protein secretion.

Main Results:

• Detectable hCG-beta-chaperone complexes correlate with folding rate and extent.
• Complexes involving ER chaperones (BiP, ERp72, ERp94) facilitate the formation of secretable hCG-beta.
• Binding between hCG-beta and chaperones involves the formation of intermolecular disulfide bonds.

Conclusions:

• Chaperone complex formation is linked to the folding kinetics of hCG-beta, not solely to glycosylation status.
• These chaperone interactions are productive, guiding hCG-beta towards secretion.
• Intermolecular disulfide bond formation is a key feature of hCG-beta-chaperone binding.