Methylation of Salmonella Typhimurium flagella promotes bacterial adhesion and host cell invasion

Julia A Horstmann,Caroline Kühne,Hélène Cazzola,Claire Rossi,Ravi K Lokareddy,Marc Erhardt,Pascal Steffen,Yannick Rossez,Kelly T Hughes,Guntram A Grassl,Theresia E B Stradal,Laurine Lemaire,Johannes Heidemann,Charlotte Uetrecht,Sandra Szefs,Michele Lunelli,Hartmut Schlüter,Michael Kolbe,Chu Wang

doi:10.1038/s41467-020-15738-3

Abstract

The long external filament of bacterial flagella is composed of several thousand copies of a single protein, flagellin. Here, we explore the role played by lysine methylation of flagellin in Salmonella, which requires the methylase FliB. We show that both flagellins of Salmonella enterica serovar Typhimurium, FliC and FljB, are methylated at surface-exposed lysine residues by FliB. A Salmonella Typhimurium mutant deficient in flagellin methylation is outcompeted for gut colonization in a gastroenteritis mouse model, and methylation of flagellin promotes bacterial invasion of epithelial cells in vitro. Lysine methylation increases the surface hydrophobicity of flagellin, and enhances flagella-dependent adhesion of Salmonella to phosphatidylcholine vesicles and epithelial cells. Therefore, posttranslational methylation of flagellin facilitates adhesion of Salmonella Typhimurium to hydrophobic host cell surfaces, and contributes to efficient gut colonization and host infection.

Highlights

The long external filament of bacterial flagella is composed of several thousand copies of a single protein, flagellin
We demonstrate that FliB-mediated flagellin methylation is crucial for Salmonella pathogenesis in the mouse model and contributes significantly to adhesion and invasion of epithelial cells in vitro, but does neither affect swimming motility nor flagella assembly (Fig. 3)
Analysis of the surface hydrophobicity of purified flagella revealed that methylation of the filament subunits increases the hydrophobicity of the outer surface of the flagellar filament, while the lumen of the flagellar filament seems not to be affected (Fig. 5a, b, Supplementary Fig. 9)

Summary

Introduction

The long external filament of bacterial flagella is composed of several thousand copies of a single protein, flagellin. We find that methylation of flagella facilitates adhesion of Salmonella Typhimurium to hydrophobic host cell surfaces. In order to map the identified ɛ-N-methyl-lysine residues to the structure of both flagellins, we determined the crystal structure of FljB (Fig. 1, Supplementary Note 1).

Results

Conclusion