Determinants for Substoichiometric Inhibition of IAPP and Aβ Amyloid Aggregations by Bri2 BRICHOS.

Bri2 BRICHOS, a folded domain of the transmembrane protein Bri2 expressed in both the brain and pancreas, is an experimentally known substoichiometric inhibitor of amyloid aggregation. The molecular chaperone effectively delays fibrillization at low molar ratios for both β-amyloid (Aβ) in Alzheimer's disease (AD) and islet amyloid polypeptide (IAPP) in type 2 diabetes (T2D). While discovering effective antiamyloid inhibitors that work at low doses is an appealing strategy to mitigate amyloid toxicity, the molecular mechanism underlying the broad and efficient antiamyloid activity of Bri2 BRICHOS remains unknown. Here, we computationally demonstrated that Bri2 BRICHOS exhibits a stronger binding affinity to fibril seeds than to monomers using atomistic discrete molecular dynamic simulations. By competing with monomers to bind the active elongation sites on newly nucleated, weakly populated fibril seeds, a small amount of Bri2 BRICHOS could block rapid fibril growth via monomer addition. The experimentally observed differential inhibition efficiency against IAPP and Aβ aggregation was found to depend on the relative fibril-binding affinities of the inhibitor compared to those of self-seeding monomers. Our computationally derived determinants for substoichiometric inhibition against amyloid aggregation by Bri2 BRICHOS may inform the future design of potent antiamyloid therapies for AD, T2D, and other amyloid diseases.