Competition between inside-out unfolding and pathogenic aggregation in an amyloid-forming β-propeller.

Area of Science:

• Biochemistry
• Structural Biology
• Ophthalmology

Background:

• Myocilin mutations cause glaucoma via cytotoxic intracellular aggregation.
• Amyloid fibril formation requires exposure of aggregation-prone regions, often through protein unfolding.

Purpose of the Study:

• To investigate the relationship between protein unfolding and aggregation in glaucoma-associated myocilin (OLF).
• To characterize the aggregation mechanisms of wild-type OLF and its disease variants.

Main Methods:

• Utilized chemical unfolding studies with urea to probe OLF conformational changes.
• Compared aggregation rates and intermediate structures of wild-type OLF (OLF^WT) and disease variants (OLF^D380A, OLF^I499F).

Main Results:

• Aggregation of OLF^WT competes with chemical unfolding below a critical tertiary structure loss threshold.
• Disease variants aggregate similarly to OLF^WT initially but adopt distinct partially folded structures.
• Unfolding propagates from the core to the surface of the OLF protein.

Conclusions:

• Protein unfolding and aggregation are competing processes for myocilin.
• Conformational changes are necessary for amyloid fibril formation in myocilin, influencing disease pathogenesis.