title: Soluble components of the flagellar export apparatus, FliI, FliJ, and FliH, do not deliver flagellin, the major filament protein, from the cytosol to the export gate.
abstract: Flagella, the locomotion organelles of bacteria, extend from the cytoplasm to the cell exterior. External flagellar proteins are synthesized in the cytoplasm and exported by the flagellar type III secretion system. Soluble components of the flagellar export apparatus, FliI, FliH, and FliJ, have been implicated to carry late export substrates in complex with their cognate chaperones from the cytoplasm to the export gate. The importance of the soluble components in the delivery of the three minor late substrates FlgK, FlgL (hook-filament junction) and FliD (filament-cap) has been convincingly demonstrated, but their role in the transport of the major filament component flagellin (FliC) is still unclear. We have used continuous ATPase activity measurements and quartz crystal microbalance (QCM) studies to characterize interactions between the soluble export components and flagellin or the FliC:FliS substrate-chaperone complex. As controls, interactions between soluble export component pairs were characterized providing Kd values. FliC or FliC:FliS did not influence the ATPase activity of FliI alone or in complex with FliH and/or FliJ suggesting lack of interaction in solution. Immobilized FliI, FliH, or FliJ did not interact with FliC or FliC:FliS detected by QCM. The lack of interaction in the fluid phase between FliC or FliC:FliS and the soluble export components, in particular with the ATPase FliI, suggests that cells use different mechanisms for the export of late minor substrates, and the major substrate, FliC. It seems that the abundantly produced flagellin does not require the assistance of the soluble export components to efficiently reach the export gate.
authors: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt. 2, H-1117 Budapest, Hungary.
authors: Ráchel
authors: R
authors: Sajó
authors: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt. 2, H-1117 Budapest, Hungary.
authors: Károly
authors: K
authors: Liliom
authors: Bio-Nanosystems Laboratory, Faculty of Information Technology, University of Pannonia, Egyetem u. 10, H-8200 Veszprém, Hungary.
authors: Adél
authors: A
authors: Muskotál
authors: Bio-Nanosystems Laboratory, Faculty of Information Technology, University of Pannonia, Egyetem u. 10, H-8200 Veszprém, Hungary.
authors: Agnes
authors: A
authors: Klein
authors: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt. 2, H-1117 Budapest, Hungary.
authors: Péter
authors: P
authors: Závodszky
authors: Bio-Nanosystems Laboratory, Faculty of Information Technology, University of Pannonia, Egyetem u. 10, H-8200 Veszprém, Hungary.
authors: Ferenc
authors: F
authors: Vonderviszt
authors: Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt. 2, H-1117 Budapest, Hungary. Electronic address: dobo.jozsef@ttk.mta.hu.
authors: József
authors: J
authors: Dobó
keywords: Flagellar export; Flagellin; FliI ATPase; FliS chaperone; Late export substrate; Type III secretion