Proteolytically inactive insulin-degrading enzyme inhibits amyloid formation yielding non-neurotoxic ABeta peptide aggregates

Abstract

Insulin-degrading enzyme (IDE) is a neutral Zn(2+) peptidase that degrades short peptides based on substrate conformation, size and charge. Some of these substrates, including amyloid â (Aâ) are capable of self-assembling into cytotoxic oligomers. Based on IDE recognition mechanism and our previous report of the formation of a stable complex between IDE and intact Aâ in vitro and in vivo, we analyzed the possibility of a chaperone-like function of IDE. A proteolytically inactive recombinant IDE with Glu111 replaced by Gln (IDEQ) was used. IDEQ blocked the amyloidogenic pathway of Aâ yielding non-fibrillar structures as assessed by electron microscopy. Measurements of the kinetics of Abeta aggregation by light scattering showed that 1) IDEQ effect was promoted by ATP independent of its hydrolysis, 2) end products of Abeta-IDEQ co-incubation were incapable of "seeding" the assembly of monomeric Abeta and 3) IDEQ was ineffective in reversing Aâ aggregation. Moreover, Abeta aggregates formed in the presence of IDEQ were non-neurotoxic. IDEQ had no conformational effects upon insulin (a non-amyloidogenic protein under physiological conditions) and did not disturb insulin receptor activation in cultured cells. Our results suggest that IDE has a chaperone-like activity upon amyloid-forming peptides. It remains to be explored whether other highly conserved metallopeptidases have a dual protease-chaperone function to prevent the formation of toxic peptide oligomers from bacteria to mammals.