Aggregation Interplay between Variants of the RepA-WH1 Prionoid in Escherichia coli

The N-terminal domain (winged-helix domain, orWH1) of the Pseudomonas pPS10 plasmid DNA replication protein RepA can assemble into amyloid fibers in vitro and, when expressed in Escherichia coli, leads to a unique intracellular amyloid pro-teinopathy by hampering bacterial proliferation. RepA-WH1 amyloidosis propagates along generations through the transmis-sion of aggregated particles across the progeny, but it is unable to propagate horizontally as an infectious agent and is thus the first synthetic bacterial prionoid. RepA-WH1 amyloidosis is promoted by binding to double-stranded DNA (dsDNA) in vitro, and it is modulated by the Hsp70 chaperone DnaK in vivo. Different mutations in the repA-WH1 gene result in variants of the protein with distinct amyloidogenic properties. Here, we report that intracellular aggregates of the hyperamyloidogenic RepA with an A31V change inWH1 [RepA-WH1(A31V)] are able to induce and enhance the growth in vivo of new amyloid particles frommolecules of wild-type RepA-WH1 [RepA-WH1(WT)], which otherwise would remain soluble in the cytoplasm. In con-trast, RepA-WH1(N37), a variant lacking a clear amyloidogenic sequence stretch that aggregates as conventional inclusion bodies (IBs), can drive the aggregation of the soluble protein into IBs only if expressed at high molar ratios over RepA-WH1(WT). The cytotoxic bacterial intracellular prionoid RepA-WH1 thus exhibits a hallmark feature of amyloids, as character-ized in eukaryotes: cross-aggregation between variants of the same protein. Amyloid proteinopathies are neurodegenerative and systemicdiseases with increasing incidence in human population and are currently one of the main burdens associated with aging. Al