Hook‐basal‐body assembly state dictates substrate specificity of the flagellar type‐III secretion system

Abstract

Many bacteria move in liquid environments using a macromolecular propeller, the flagellum. A type-III secretion system (T3SS) at the base of the flagellum and the related injectisome of Gram-negative pathogens are required to build and operate these sophisticated nanomachines. The flagellar structure can be divided into three main parts:(a) a cell envelope-anchored basal body (consisting of the C-ring, the flagellar-specific T3SS, the MS-ring, the rod and the LP-ring), (b) a hook and, (c) a filament. Secretion of a variety of different T3SS substrate proteins occurs from the cytoplasm to the distal end of the growing structure in a highly regulated and sequential manner (Chevance & Hughes, 2008;Diepold & Wagner, 2014;Wagner et al., 2018). The different secretion substrates of the flagellar T3SS (fT3SS) have been

FlhE functions as a chaperone to prevent formation of periplasmic flagella in Gram-negative bacteria

“…fT3SS mutants locked in early- mode secretion, by either using the presence of an allele of FlhB unable to undergo auto-catalytic cleavage (FlhBN269A) 22 , or a deletion of the gene of the molecular ruler FliK, also presented a WT phenotype on GP. Finally, blocking secretion of substrates via the fT3SS using a non-translocatable FliC-GFP translational fusion 23,24 resulted in a WT phenotype on GP. Cell lysis was independent of the flagellin composition of the filament (FliC-ON/FljB-ON) 25,26 , as well as filament rotation as a deletion (Δ motAB ) or non-functional mutant (MotAM206A/MotBD33A) of the stator units did not restore the WT phenotype 27 (Fig.…”

FlhE functions as a chaperone to prevent formation of periplasmic flagella in Gram-negative bacteria

“…fT3SS mutants locked in early-mode secretion, by either using the presence of an allele of FlhB unable to undergo auto-catalytic cleavage (FlhB N269A ) 24 , or a deletion of the gene of the molecular ruler FliK, also presented a WT phenotype on GP. Finally, blocking secretion of substrates via the fT3SS using a non-translocatable FliC-GFP translational fusion 25 , 26 resulted in a WT phenotype on GP. Cell lysis was independent of the flagellin composition of the filament (FliC-ON/FljB-ON) 27 , 28 , as well as filament rotation as a deletion (∆ motAB ) or non-functional mutant (MotA M206A /MotB D33A ) of the stator units did not restore the WT phenotype 29 (Fig.…”