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J. Bacteriol. doi:10.1128/JB.01710-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Characterization of the periplasmic domain of MotB and implications for its role in the stator assembly of the bacterial flagellar motor

Dynamic NanoMachine Project, ICORP, JST, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan and Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan

^* To whom correspondence should be addressed. Email: 4seiji{at}bunshi4.bio.nagoya-u.ac.jp.

	Abstract

MotA and MotB are integral membrane proteins that form the stator complex of the proton-driven bacterial flagellar motor. The stator complex functions as a proton channel and couples proton flow with torque generation. The stator must be anchored to an appropriate place of the motor, which is believed to occur through a putative peptidoglycan-binding (PGB) motif within the C-terminal periplasmic domain of MotB. In this study, we constructed and characterized an N-terminally truncated variant of Salmonella enterica serovar Typhimurium MotB consisting of residues 78 through 309 (MotB_C). MotB_C significantly inhibited motility of wild-type cells when exported into the periplasm. Some point mutations in the PGB motif enhanced the motility inhibition, while an in-frame deletion variant MotB_C(197-210) showed a significantly reduced inhibitory effect. Wild-type MotB_C and its point mutant variants formed stable homodimer while the deletion variant was monomeric. A small amount of MotB was co-isolated only with the secreted form of MotB_C-His₆ by Ni-NTA affinity chromatography, suggesting that the motility inhibition results from MotB-MotB_C heterodimer formation in the periplasm. However, the monomeric mutant variant MotB_C(197-210) did not bind to MotB, suggesting that MotB_C is directly involved in the stator assembly. We propose that the MotB_C dimer domain plays an important role in targeting and stable anchoring of the MotA/MotB complex to putative stator-binding sites of the motor.

This article has been cited by other articles:

• Roujeinikova, A. (2008). Crystal structure of the cell wall anchor domain of MotB, a stator component of the bacterial flagellar motor: Implications for peptidoglycan recognition. Proc. Natl. Acad. Sci. USA 105: 10348-10353 [Abstract] [Full Text]