RepA-WH1 prionoid: Clues from bacteria on factors governing phase transitions in amyloidogenesis

ABSTRACT

In bacterial plasmids, Rep proteins initiate DNA replication by undergoing a structural transformation coupled to dimer dissociation. Amyloidogenesis of the ‘winged-helix’ N-terminal domain of RepA (WH1) is triggered in vitro upon binding to plasmid-specific DNA sequences, and occurs at the bacterial nucleoid in vivo. Amyloid fibers are made of distorted RepA-WH1 monomers that assemble as single or double intertwined tubular protofilaments. RepA-WH1 causes in E. coli an amyloid proteinopathy, which is transmissible from mother to daughter cells, but not infectious, and enables conformational imprinting in vitro and in vivo; i.e. RepA-WH1 is a ‘prionoid’. Microfluidics allow the assessment of the intracellular dynamics of RepA-WH1: bacterial lineages maintain two types (strains-like) of RepA-WH1 amyloids, either multiple compact cytotoxic particles or a single aggregate with the appearance of a fluidized hydrogel that it is mildly detrimental to growth. The Hsp70 chaperone DnaK governs the phase transition between both types of RepA-WH1 aggregates in vivo, thus modulating the vertical propagation of the prionoid. Engineering chimeras between the Sup35p/[PSI⁺] prion and RepA-WH1 generates [REP-PSI⁺], a synthetic prion exhibiting strong and weak phenotypic variants in yeast. These recent findings on a synthetic, self-contained bacterial prionoid illuminate central issues of protein amyloidogenesis.

KEYWORDS:

• amyloid proteinopathy
• amyloid polymorphism
• bacterial prionoid
• Hsp70 chaperone
• phase transitions
• RepA-WH1

This article refers to:

DISCLOSURE OF POTENTIAL CONFLICTS OF INTEREST

No potential conflicts of interest were disclosed.

Acknowledgments

We are indebted to our colleagues who originally contributed to the work reviewed here, especially to M.E. Fernández-Tresguerres, A. Serrano and F. Gasset-Rosa, as well as to A. Lindner, O. Llorca, F. Moreno-Herrero and their co-workers.

Funding

Research on RepA-WH1 amyloids at CIB-CSIC is currently financed by Spanish MINECO grants BIO2012-30852 and CSD2009-00088.