Structure of the bacterial flagellar protofilament and implications for a switch for supercoiling

Nature. 2001 Mar 15;410(6826):331-7. doi: 10.1038/35066504.


The bacterial flagellar filament is a helical propeller constructed from 11 protofilaments of a single protein, flagellin. The filament switches between left- and right-handed supercoiled forms when bacteria switch their swimming mode between running and tumbling. Supercoiling is produced by two different packing interactions of flagellin called L and R. In switching from L to R, the intersubunit distance ( approximately 52 A) along the protofilament decreases by 0.8 A. Changes in the number of L and R protofilaments govern supercoiling of the filament. Here we report the 2.0 A resolution crystal structure of a Salmonella flagellin fragment of relative molecular mass 41,300. The crystal contains pairs of antiparallel straight protofilaments with the R-type repeat. By simulated extension of the protofilament model, we have identified possible switch regions responsible for the bi-stable mechanical switch that generates the 0.8 A difference in repeat distance.

MeSH terms

  • Crystallography, X-Ray
  • Flagellin / chemistry*
  • Flagellin / genetics
  • Flagellin / metabolism
  • Models, Molecular
  • Molecular Motor Proteins
  • Mutation
  • Peptide Fragments / chemistry
  • Peptide Fragments / genetics
  • Peptide Fragments / metabolism
  • Protein Conformation
  • Protein Transport
  • Salmonella typhimurium / chemistry


  • Molecular Motor Proteins
  • Peptide Fragments
  • Flagellin

Associated data

  • PDB/1IO1