Amino‐terminal residues dictate the export efficiency of the Campylobacter jejuni filament proteins via the flagellum

Abstract

SummaryBacterial flagella play an essential role in the pathogenesis of numerous enteric pathogens. The flagellum is required for motility, colonization, and in some instances, for the secretion of effector proteins. In contrast to the intensively studied flagella of Escherichia coli and Salmonella typhimurium, the flagella of Campylobacter jejuni, Helicobacter pylori and Vibrio cholerae are less well characterized and composed of multiple flagellin subunits. This study was performed to gain a better understanding of flagellin export from the flagellar type III secretion apparatus of C. jejuni. The flagellar filament of C. jejuni is comprised of two flagellins termed FlaA and FlaB. We demonstrate that the amino-termini of FlaA and FlaB determine the length of the flagellum and motility of C. jejuni. We also demonstrate that protein-specific residues in the amino-terminus of FlaA and FlaB dictate export efficiency from the flagellar type III secretion system (T3SS) of Yersinia enterocolitica. These findings demonstrate that key residues within the amino-termini of two nearly identical proteins influence protein export efficiency, and that the mechanism governing the efficiency of protein export is conserved among two pathogens belonging to distinct bacterial classes. These findings are of additional interest because C. jejuni utilizes the flagellum to export virulence proteins.

Secretion of Flagellar Proteins by the Pseudomonas aeruginosa Type III Secretion-Injectisome System

“…The secretion signal for substrates of the injectisomeand flagellum-T3SSs is typically located within the first 15 to 20 amino-terminal residues (35)(36)(37). To examine the requirements for FliC secretion, we fused full-length FliC (FliC 1-394 -CyaA) or the first 20 amino-terminal residues of FliC (FliC 1-20 -CyaA) to a truncated form of the calmodulin-dependent adenylate cyclase domain (ϳ50 kDa) from Bordetella pertussis CyaA.…”

Extracellular secretion of protease HtrA fromCampylobacter jejuniis highly efficient and independent of its protease activity and flagellum

“…A tempting hypothesis was that HtrA maybe secreted into the extracellular milieu using the fl agellum as it has been shown for CiaB and other C. jejuni factors [10][11][12][13]. To test this idea, C. jejuni wt strain 81-176 and its isogenic fl agellar mutants Δfl aA/B, Δfl iI, Δfl gH, Δfl hA, Δfl hB, and Δfl gS [32][33][34] were subjected to HtrA secretion assays as described above.…”

“…A series of papers reported on the extracellular release of C. jejuni proteins into the medium in the presence of fetal calf serum (FCS) or upon host cell contact, which was abrogated when certain fl agellar genes were mutated. This led some groups to propose that the C. jejuni fl agellum may act as a classical type III secretion system (T3SS) for the extracellular transport or injection of proteins, which then infl uence bacterial-host interactions [10][11][12][13]. The fi rst identifi ed secreted factor depending on the fl agellum was the Campylobacter invasion antigen B (CiaB), a 73-kDa protein with weak homology to T3SS effectors of other pathogens [11].…”

Two Residues Predominantly Dictate Functional Difference in Motility between Shewanella oneidensis Flagellins FlaA and FlaB

“…In cases reported thus far, this scenario is attributable to flagellin regulation of various levels, including transcription, translation, post-translational modification, secretion, and filament assembly (4,7,(12)(13)(14)(15)(16)(17).…”