Multitasking of Hsp70 chaperone in the biogenesis of bacterial functional amyloids

Shinya Sugimoto,Akari Terao,Ken-Ichi Arita-Morioka,Kunitoshi Yamanaka,Teru Ogura,Yoshimitsu Mizunoe

doi:10.1038/s42003-018-0056-0

Shinya Sugimoto, Akari Terao + Show 4 more

Open Access

https://doi.org/10.1038/s42003-018-0056-0

Copy DOI

Abstract

Biofilms are intricate communities of microorganisms embedded in a self-produced matrix of extracellular polymer, which provides microbes survival advantages in stressful environments and can cause chronic infections in humans. Curli are functional amyloids that assemble on the extracellular surface of enteric bacteria such as Escherichia coli during biofilm development and colonization. The molecular chaperone DnaK, a bacterial Hsp70 homologue, promotes curli biogenesis via unknown mechanism(s). Here we show that DnaK increases the expression of CsgA and CsgB—the major and minor structural components of curli, respectively—via a quantity and quality control of RpoS, a stationary phase-specific alternative sigma factor regulating bacterial transcription, and CsgD, the master transcriptional regulator of curli formation. DnaK also keeps CsgA and CsgB in a translocation-competent state by binding to their signal peptides prone to aggregation. Our findings suggest that DnaK controls the homoeostasis of curli biogenesis at multiple stages to organize the biofilm matrix.

Highlights

Biofilms are intricate communities of microorganisms embedded in a self-produced matrix of extracellular polymer, which provides microbes survival advantages in stressful environments and can cause chronic infections in humans
Unlike pathogenic amyloids that result from protein misfolding, curli are generated via a secretory nucleation-precipitation mechanism or the type VIII secretion system[7]; in Escherichia coli, seven proteins encoded by two operons—curli-specific genes BAC and DEFG—regulate curli expression, export, and assembly[8]
Our findings indicate that DnaK has a multifunctional role in bacterial amyloid biogenesis

Summary

Introduction

Biofilms are intricate communities of microorganisms embedded in a self-produced matrix of extracellular polymer, which provides microbes survival advantages in stressful environments and can cause chronic infections in humans. Expression of a plasmid-borne wild type DnaK (DnaKWT) complemented the biofilm formation and curli production deficiencies of the ΔdnaK strain (Fig. 1e).

Results

Conclusion