Amyloid cannot resist identification

Abstract

The capacity to polymerize into amyloid fibrils is common to many proteins. While some proteins naturally form these fibrils to serve functional roles, amyloid is usually associated with pathogenic processes in which specific proteins aberrantly aggregate within cells or tissues. Though the contribution of amyloid fibrils to actual disease pathogenesis is not always clear, one possibility is that the titration of essential proteins from solution into aggregates contributes to the cellular degeneration common to many amyloid diseases. Using mammalian and yeast model systems, we recently showed that the common biophysical properties of amyloid aggregates--including strong resistance to dissolution--enable stringent purification and identification of both amyloid-forming and amyloid-associated proteins directly from cells. Strikingly, many proteins that were previously implicated in formation or clearance of intracellular aggregates, including several stress granule components, were found to co-aggregate with amyloid formed by a polyglutamine-expanded huntingtin fragment. This direct evaluation of proteins within aggregates can help identify new amyloid-forming proteins, as well as proteins that can indirectly contribute to disease mechanisms.

Keywords: amyloid; polyglutamine; prion; protein aggregation; yeast.

Figure 1. Cartoon representation of an isogenic pair of yeast cells. The cell on the right harbors an amyloid aggregate. TAPI (technique for amyloid purification and identification) couples a novel purification scheme with tandem mass spectrometry to identify proteins that form amyloid or are tightly associated with amyloid aggregates.