Extracellular transfer of a conserved polymerization factor for multi-flagellin filament assembly in Caulobacter

Interconversion of tripartite and bipartite systems for site-specificO-sialylation of flagellin in Gram-negative and Gram-positive bacteria

“…While these flagellin binding proteins reside in the cytoplasm, there are others such as the innate immune receptor TLR5 40,41 or flagellin capping proteins that must bind flagellin in the extra- cytoplasmic space 11 . Capping proteins or analogous flagellin polymerization factors 12 act as chaperones that promote the insertion of flagellin at the distal end of the flagellar filament, once the unfolded flagellins emerge at the end of the secretion tunnel inside the flagellar filament following their export from the bacterial cytoplasm 11,12,42 . To ensure that they are located at the distal end of the nascent filament before the flagellins arrive, capping proteins are thought to be secreted through the flagellar translocation apparatus before the flagellins (are expressed) 12 .…”

“…Capping proteins or analogous flagellin polymerization factors 12 act as chaperones that promote the insertion of flagellin at the distal end of the flagellar filament, once the unfolded flagellins emerge at the end of the secretion tunnel inside the flagellar filament following their export from the bacterial cytoplasm 11,12,42 . To ensure that they are located at the distal end of the nascent filament before the flagellins arrive, capping proteins are thought to be secreted through the flagellar translocation apparatus before the flagellins (are expressed) 12 . By contrast, flagellin can only bind TLR5 in the extracellular space upon dissociation from the filament or upon escape from the capping/polymerization protein.…”

“…For transmission electron microscopy (TEM), S. oneidensis cells were negatively stained with uranyl acetate using a previously described protocol 12,16 . Briefly, cells were harvested after 4 hours of growth and resuspended in sterile water.…”

“…The surface exposed hook functions as a flexible joint that transmits torque from the rotor to the long flagellar filament that acts as a propeller. For filament assembly to occur, dedicated secretion chaperones direct flagellin subunits through the hollow conduit in the hook-basal-body (HBB) traversing the PG layer where they are received by specialized polymerization chaperones 11,12 , also known as capping proteins, located at the tip of the nascent filament. These polymerization chaperones catalyse the sequential incorporation of flagellin at the distal tip, forming a tubular filament composed of 11 protofilaments adopting different superhelical states 13 .…”

Subtilase SBT5.2 inactivates flagellin immunogenicity in the plant apoplast

“…Indeed, the fliD mutant of Pta6604 secreted large amounts of monomeric flagellin and triggers strong immune responses (Shimizu et al, 2003). Third, flagella are shed upon starvation and during the cell cycle (Zhu & Gao 2020; Kint & Viollier 2023;Yonekura et al, 2000;Kostyukova et al, 1988), and although flagella do not depolymerise (Aizawa et al, 1990), they might release monomers when incubated in an apoplastic environment. Fourth, damage of the flagellin filament, e.g.…”