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Title: Substrate-specific export chaperones mediating bacterial flagellum assembly
Author: Bennett, J. C. Q.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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During flagellum assembly by motile enterobacteria, the highly helical flagellar proteins destined for polymerization into the growing cell surface structure are exported through a small channel at the core of the flagellum, but the mechanism preventing their premature folding and oligomerization in the cytosol remained unknown. This thesis addresses this issue by characterizing the roles of FlgN and FliT, two flagellar proteins of previously undetermined function. Affinity blotting of radiolabelled FlgN to Proteus mirabilis or Salmonella typhimurium cell extracts indicated that it binds to two flagellar proteins. Comparative blotting of proteins secreted by wild-type S. typhimurium and specific flagellar mutants suggested that FlgN binds the flagellar hook-associated proteins (HAPs) FlgK and FlgL. This was confirmed by FlgN binding to each HAP, following their artificial expression in Escherichia coli. Export of FlgK and FlgL was specifically reduced in a S. typhimurium flgN mutant, concomitant with increased release of FliC and FliD, the immediately distal components of the flagellum. Comparable experiments showed that FliT binds specifically to the third HAP, FliD. Removal of HAP C-terminal domains abolished binding to FlgN and FliT, and polypeptides comprising each of the HAP C-termini were specifically bound by FlgN and FliT. The data suggest that FlgN and FliT are specialized substrate-specific chaperones that act as 'bodyguards' to shield interactive surfaces of their targets prior to export.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available