POSTERS - BLAST X - University of Utah

BLAST X Tue. Morning Session
STRUCTURAL INSIGHT INTO ACTIVE FLAGELLAR MOTOR FORMATION THROUGH THE
PERIPLASMIC REGION OF MOTB
Seiji Kojima 1 , Mayuko Sakuma 1 , Yuki Sudo 1 , Chojiro Kojima 2 , Tohru Minamino 3 , Keiichi
Namba 3 , Michio Homma 1 and Katsumi Imada 3*
1 Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-Ku,
Nagoya 464-8602, Japan; 2 Laboratory of Biophysics, Graduate School of Biological Sciences,
Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara, 630-0192
Japan; 3 Graduate School of Frontier Biosciences, Osaka University, 1-3 Yamadaoka, Suita,
Osaka 565-0871, Japan
Bacterial flagellar motor is a supramolecular nano-machine powered by the
transmembrane gradient of protons or sodium ions, and spins flagellar filaments to drive cell
motility. Motor torque is generated by the rotor-stator interaction that is coupled with ion flow
through the ion-channel in the stator unit, which is composed of four MotA and two MotB
subunits. About ten stators are assembled around the perimeter of the rotor and anchored to
peptidoglycan layer by the peptidoglycan-binding (PGB) domain of MotB. The rotor-stator
assembly is not a rigid complex, so each stator unit can dynamically be exchanged in the
functional motor, and is activated only when assembled around the rotor. However, the
mechanisms of the stator assembly and the activation of the proton flow remain unclear. Here,
we report the crystal structure of a C-terminal fragment of MotB (MotBC), which includes the
PGB domain and covers the whole periplasmic region essential for cell motility (PEM), at 1.75 Å
resolution. The structure, and subsequent mutational and biochemical analyses indicate that
dimer formation by the PGB domains is required for motility through the regulation of the
arrangement of the transmembrane segment. Moreover, we show that large structural changes
in the N-terminal helices should be coupled with both peptidoglycan binding and activation of
the stator. This work provides novel structural insight into the dynamic behavior of the ionchannel
complex regulated by the periplasmic domain, and the activation mechanism of the
complex coupled with completion of the assembly where it works.
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