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Similar modes of polypeptide recognition by export chaperones in flagellar biosynthesis and type III secretion

Nature Structural & Molecular Biology volume 10, pages 789–793 (2003)Cite this article

Abstract

Assembly of the bacterial flagellum and type III secretion in pathogenic bacteria require cytosolic export chaperones that interact with mobile components to facilitate their secretion. Although their amino acid sequences are not conserved, the structures of several type III secretion chaperones revealed striking similarities between their folds and modes of substrate recognition. Here, we report the first crystallographic structure of a flagellar export chaperone, Aquifex aeolicus FliS. FliS adopts a novel fold that is clearly distinct from those of the type III secretion chaperones, indicating that they do not share a common evolutionary origin. However, the structure of FliS in complex with a fragment of FliC (flagellin) reveals that, like the type III secretion chaperones, flagellar export chaperones bind their target proteins in extended conformation and suggests that this mode of recognition may be widely used in bacteria.

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Figure 1: The structure of Aquifex aeolicus FliS is unrelated to those of the type III secretion chaperones.
Figure 2: Limited proteolysis of FliS-His6 in the presence and absence of FliC(427–518).
Figure 3: FliS and SycE bind their targets in an extended conformation.
Figure 4: Gln505 of FliC and Tyr8 of FliS occupy equivalent positions in the hydrophobic pocket of FliS.
Figure 5: Structure-based sequence alignments of FliS and FliC proteins from various bacterial species with residues numbered according to the A. aeolicus proteins.

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Acknowledgements

We thank SBL Biophysics Core Resource (US National Cancer Institute at Frederick) for the use of the electrospray mass spectrometer and the Protein Chemistry Laboratory (SAIC-Frederick) for amino acid sequencing. Data were collected at beamlines 17-ID and 17-BM in the facilities of the Industrial Macromolecular Crystallography Association Collaborative Access Team (IMCA-CAT) at the Advanced Photon Source.

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  1. Artem G Evdokimov & Matthew Pokross

    Present address: Procter & Gamble Pharmaceuticals, Health Care Research Center-Discovery, 8700 Mason-Montgomery Road, Mason, Ohio, 45040-9462, USA

Authors and Affiliations

  1. Macromolecular Crystallography Laboratory, Center for Cancer Research, National Cancer Institute at Frederick, PO Box B, Frederick, 21702-1201, Maryland, USA

    Artem G Evdokimov, Jason Phan, Joseph E Tropea, Karen M Routzahn, Howard K Peters III, Matthew Pokross & David S Waugh

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Correspondence to David S Waugh.

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Evdokimov, A., Phan, J., Tropea, J. et al. Similar modes of polypeptide recognition by export chaperones in flagellar biosynthesis and type III secretion. Nat Struct Mol Biol 10, 789–793 (2003). https://doi.org/10.1038/nsb982

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