The Amyloid Region of Hfq Riboregulator Promotes DsrA:rpoS RNAs Annealing

SIMPLE SUMMARY: RNA:amyloid protein interactions have been observed in the past few years. Nevertheless, the molecular basis and physiological implications of these interactions are still poorly understood. Here we focus on a bacterial amyloid protein, Hfq. This protein is a pleiotropic bacterial regulator that mediates many aspects of RNA metabolism. The protein notably mediates mRNA stability and translation efficiency by using stress-related small noncoding regulatory RNAs. This regulation contributes to bacterial adaptation to stresses. Our results show that the amyloid region of Hfq significantly influences the efficiency of annealing between DsrA small noncoding RNA to its target mRNA. This unexpected result opens perspectives for a novel physiological role of amyloids, including those associated with neurodegenerative diseases. ABSTRACT: Hfq is a bacterial RNA chaperone which promotes the pairing of small noncoding RNAs to target mRNAs, allowing post-transcriptional regulation. This RNA annealing activity has been attributed for years to the N-terminal region of the protein that forms a toroidal structure with a typical Sm-fold. Nevertheless, many Hfqs, including that of Escherichia coli, have a C-terminal region with unclear functions. Here we use a biophysical approach, Synchrotron Radiation Circular Dichroism (SRCD), to probe the interaction of the E. coli Hfq C-terminal amyloid region with RNA and its effect on RNA annealing. This C-terminal region of Hfq, which has been described to be dispensable for sRNA:mRNA annealing, has an unexpected and significant effect on this activity. The functional consequences of this novel property of the amyloid region of Hfq in relation to physiological stress are discussed.