Recognition and targeting mechanisms by chaperones in flagellum assembly and operation

Nandish Khanra, Paolo Rossi, Anastassios Economou, Charalampos G. Kalodimos

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


The flagellum is a complex bacterial nanomachine that requires the proper assembly of several different proteins for its function. Dedicated chaperones are central in preventing aggregation or undesired interactions of flagellar proteins, including their targeting to the export gate. FliT is a key flagellar chaperone that binds to several flagellar proteins in the cytoplasm, including its cognate filament-capping protein FliD. We have determined the solution structure of the FliT chaperone in the free state and in complex with FliD and the flagellar ATPase FliI. FliT adopts a four-helix bundle and uses a hydrophobic surface formed by the first three helices to recognize its substrate proteins. We show that the fourth helix constitutes the binding site for FlhA, a membrane protein at the export gate. In the absence of a substrate protein FliT adopts an autoinhibited structure wherein both the binding sites for substrates and FlhA are occluded. Substrate binding to FliT activates the complex for FlhA binding and thus targeting of the chaperone-substrate complex to the export gate. The activation and targeting mechanisms reported for FliT appear to be shared among the other flagellar chaperones.

Original languageEnglish (US)
Pages (from-to)9798-9803
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number35
StatePublished - Aug 30 2016

Bibliographical note

Funding Information:
This work was supported by NIH Grant AI094623 (to C.G.K.) and Fonds Wetenschappelijk Onderzoek Grant T3RecS G002516N (to A.E.).


  • Assembly factors
  • Chaperones
  • Flagellum
  • Nmr spectroscopy
  • Type III secretion


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