Kinetic characterization of Salmonella FliK-FlhB interactions demonstrates complexity of the Type III secretion substrate-specificity switch.

Journal Article (Journal Article)

The bacterial flagellum is a complex macromolecular machine consisting of more than 20 000 proteins, most of which must be exported from the cell via a dedicated Type III secretion apparatus. At a defined point in flagellar morphogenesis, hook completion is sensed and the apparatus switches substrate specificity type from rod and hook proteins to filament ones. How the switch works is a subject of intense interest. FliK and FlhB play central roles. In the present study, two optical biosensing methods were used to characterize FliK-FlhB interactions using wild-type and two variant FlhBs from mutants with severe flagellar structural defects. Binding was found to be complex with fast and slow association and dissociation components. Surprisingly, wild-type and variant FlhBs had similar kinetic profiles and apparent affinities, which ranged between 1 and 10.5 microM, suggesting that the specificity switch is more complex than presently understood. Other binding experiments provided evidence for a conformational change after binding. Liquid chromatography-mass spectrometry (LC-MS) and NMR experiments were performed to identify a cyclic intermediate product whose existence supports the mechanism of autocatalytic cleavage at FlhB residue N269. The present results show that while autocatalytic cleavage is necessary for proper substrate specificity switching, it does not result in an altered interaction with FliK, strongly suggesting the involvement of other proteins in the mechanism.

Full Text

Duke Authors

Cited Authors

  • Morris, DP; Roush, ED; Thompson, JW; Moseley, MA; Murphy, JW; McMurry, JL

Published Date

  • August 3, 2010

Published In

Volume / Issue

  • 49 / 30

Start / End Page

  • 6386 - 6393

PubMed ID

  • 20586476

Pubmed Central ID

  • PMC2912450

Electronic International Standard Serial Number (EISSN)

  • 1520-4995

Digital Object Identifier (DOI)

  • 10.1021/bi100487p


  • eng

Conference Location

  • United States