Role of flagellar hydrogen bonding in Salmonella motility and flagellar polymorphic transition

• Published in: Molecular microbiology 2019-11, Vol.112 (5), p.1519-1530
• Main Authors: Wang, Chu, Lunelli, Michele, Zschieschang, Erik, Bosse, Jens Bernhard, Thuenauer, Roland, Kolbe, Michael
• Format: Article
• Language: English
• Subjects: Bacteria; Chemical bonds; Filaments; Flagella; Flagella - metabolism; Flagellin; Flagellin - chemistry; Flagellin - genetics; Hydrogen; Hydrogen Bonding; Locomotion - genetics; Locomotion - physiology; Motility; Mutants; Residues; Salmonella; Salmonella typhimurium - physiology; Site-directed mutagenesis; Transportation networks
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.14377

Summary Bacterial flagellar filaments are assembled by tens of thousands flagellin subunits, forming 11 helically arranged protofilaments. Each protofilament can take either of the two bistable forms L‐type or R‐type, having slightly different conformations and inter‐protofilaments interactions. By mixing different ratios of L‐type and R‐type protofilaments, flagella adopt multiple filament polymorphs and promote bacterial motility. In this study, we investigated the hydrogen bonding networks at the flagellin crystal packing interface in Salmonella enterica serovar typhimurium (S. typhimurium) by site‐directed mutagenesis of each hydrogen bonded residue. We identified three flagellin mutants D108A, N133A and D152A that were non‐motile despite their fully assembled flagella. Mutants D108A and D152A trapped their flagellar filament into inflexible right‐handed polymorphs, which resemble the previously predicted 3L/8R and 4L/7R helical forms in Calladine’s model but have never been reported in vivo. Mutant N133A produces floppy flagella that transform flagellar polymorphs in a disordered manner, preventing the formation of flagellar bundles. Further, we found that the hydrogen bonding interactions around these residues are conserved and coupled to flagellin L/R transition. Therefore, we demonstrate that the hydrogen bonding networks formed around flagellin residues D108, N133 and D152 greatly contribute to flagellar bending, flexibility, polymorphisms and bacterial motility. Hydrogen bonding networks between flagellin subunits are important for flagellar polymorphic transformations and bacterial motility. Single alanine mutations of the residues D108, N133 and D152 at flagellin hydrogen bonding interface render bacterial strains with impaired motility despite flagellar assembly. The mutations D108A and D152A trapped the flagellar filament in inflexible polymorphs 3L/8R and 4L/7R. Mutant N133A produces floppy flagella that cannot form a flagellar bundle.