title: Comparative analysis of the secretion capability of early and late flagellar type III secretion substrates.
abstract: A remarkable feature of the flagellar-specific type III secretion system (T3SS) is the selective recognition of a few substrate proteins among the many thousand cytoplasmic proteins. Secretion substrates are divided into two specificity classes: early substrates secreted for hook-basal body (HBB) construction and late substrates secreted after HBB completion. Secretion was reported to require a disordered N-terminal secretion signal, mRNA secretion signals within the 5'-untranslated region (5'-UTR) and for late substrates, piloting proteins known as the T3S chaperones. Here, we utilized translational β-lactamase fusions to probe the secretion efficacy of the N-terminal secretion signal of fourteen secreted flagellar substrates in Salmonella enterica. We observed a surprising variety in secretion capability between flagellar proteins of the same secretory class. The peptide secretion signals of the early-type substrates FlgD, FlgF, FlgE and the late-type substrate FlgL were analysed in detail. Analysing the role of the 5'-UTR in secretion of flgB and flgE revealed that the native 5'-UTR substantially enhanced protein translation and secretion. Based on our data, we propose a multicomponent signal that drives secretion via the flagellar T3SS. Both mRNA and peptide signals are recognized by the export apparatus and together with substrate-specific chaperones allowing for targeted secretion of flagellar substrates.
authors.affiliation: Microbiologie, Département de Médecine, Université de Fribourg, Fribourg, Switzerland.
authors.forename: Hanna M
authors.initials: HM
authors.lastname: Singer
authors.forename: Marc
authors.initials: M
authors.lastname: Erhardt
authors.forename: Kelly T
authors.initials: KT
authors.lastname: Hughes
mesh_terms: D001089:Arabinose / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D058947:Bacterial Secretion Systems / Q000502:physiology*; D001692:Biological Transport; D005407:Flagella / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism; D014176:Protein Biosynthesis; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012486:Salmonella typhimurium / Q000378:metabolism*; D013379:Substrate Specificity; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D018832:Molecular Chaperones; D011993:Recombinant Fusion Proteins; D001089:Arabinose; D001618:beta-Lactamases