Membrane Topology of the MotA Protein ofEscherichia coil

Zhou, Jiadong; Fazzio, Robert T.; Blair, David F.

doi:10.1006/jmbi.1995.0431

Cited by 123 publications

(110 citation statements)

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“…Two types of motors, proton-driven (2) and sodium-driven (4), dependent on different coupling ions, have been described. The proton-driven motors of Escherichia coli and Salmonella typhimurium have been extensively studied, and the stator part of the torque generator consists of two cytoplasmic membrane proteins, MotA and MotB, which contain four transmembrane domains and one transmembrane domain, respectively (5)(6)(7)(8). Much genetic and physiological evidence suggests that MotA and MotB together form a proton channel (9 -13), and this complex is believed to be anchored to the cell wall via the peptidoglycan-binding domain of MotB (8,14,15).…”

Section: -Conducting Channelmentioning

confidence: 99%

Functional Reconstitution of the Na+-driven Polar Flagellar Motor Component of Vibrio alginolyticus

Sato

Homma

2000

Journal of Biological Chemistry

144

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The bacterial flagellar motor is a molecular machine that couples the influx of specific ions to the generation of the force necessary to drive rotation of the flagellar filament. Four integral membrane proteins, PomA, PomB, MotX, and MotY, have been suggested to be directly involved in torque generation of the Na ؉ -driven polar flagellar motor of Vibrio alginolyticus. In the present study, we report the isolation of the functional component of the torque-generating unit. The purified protein complex appears to consist of PomA and PomB and contains neither MotX nor MotY. The PomA/B protein, reconstituted into proteoliposomes, catalyzed 22 Na؉ influx in response to a potassium diffusion potential. Sodium uptake was abolished by the presence of Li ؉ ions and phenamil, a sodium channel blocker. This is the first demonstration of a purification and functional reconstitution of the bacterial flagellar motor component involved in torque generation. In addition, this study demonstrates that the Na ؉ -driven motor component, PomA and PomB, forms the Na ؉ -conducting channel.

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Section: -Conducting Channelmentioning

confidence: 99%

Functional Reconstitution of the Na+-driven Polar Flagellar Motor Component of Vibrio alginolyticus

Sato

Homma

2000

Journal of Biological Chemistry

144

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“…From the homology to the proton motor components and their properties (15,39,44,45,54), we expect that the four transmembrane regions of PomA and the one transmembrane region of PomB also form a complex and function as a sodium channel. An Asp residue in the transmembrane region of E. coli MotB has been proposed to act as the donor in H ϩ transfer to a recipient near the cytoplasmic side of the protein (45).…”

Section: Vol 179 1997 Genes Of Sodium-driven Flagellar Motor 5107mentioning

confidence: 99%

Putative channel components for the fast-rotating sodium-driven flagellar motor of a marine bacterium

et al. 1997

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The polar flagellum of Vibrio alginolyticus rotates remarkably fast (up to 1,700 revolutions per second) by using a motor driven by sodium ions. Two genes, motX and motY, for the sodium-driven flagellar motor have been identified in marine bacteria, Vibrio parahaemolyticus and V. alginolyticus. They have no similarity to the genes for proton-driven motors, motA and motB, whose products constitute a proton channel. MotX was proposed to be a component of a sodium channel. Here we identified additional sodium motor genes, pomA and pomB, in V. alginolyticus. Unexpectedly, PomA and PomB have similarities to MotA and MotB, respectively, especially in the predicted transmembrane regions. These results suggest that PomA and PomB may be sodium-conducting channel components of the sodium-driven motor and that the motor part consists of the products of at least four genes, pomA, pomB, motX, and motY. Furthermore, swimming speed was controlled by the expression level of the pomA gene, suggesting that newly synthesized PomA proteins, which are components of a force-generating unit, were successively integrated into the defective motor complexes. These findings imply that Na ؉ -driven flagellar motors may have similar structure and function as proton-driven motors, but with some interesting differences as well, and it is possible to compare and study the coupling mechanisms of the sodium and proton ion flux for the force generation.

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“…Each MotA (295 residues) contains four transmembrane (TM) alpha helical segments (A1-A4), two short loops in the periplasm, and two long segments (residues 61-160 and 228-295) in the cytoplasm (Fig. 1B) (3,21). Arg90 and Glu98 on the MotA cytoplasmic domain interact with the polar residues on the rotor protein, FliG, during the rotation of the motor (22,23).…”

mentioning

confidence: 99%

Gate-controlled proton diffusion and protonation-induced ratchet motion in the stator of the bacterial flagellar motor

Nishihara

Kitao

2015

Proc. Natl. Acad. Sci. U.S.A.

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The proton permeation process of the stator complex MotA/B in the flagellar motor of Escherichia coli was investigated. The atomic model structure of the transmembrane part of MotA/B was constructed based on the previously published disulfide cross-linking and tryptophan scanning mutations. The dynamic permeation of hydronium/ sodium ions and water molecule through the channel formed in MotA/B was observed using a steered molecular dynamics simulation. During the simulation, Leu46 of MotB acts as the gate for hydronium ion permeation, which induced the formation of water wire that may mediate the proton transfer to Asp32 on MotB. Free energy profiles for permeation were calculated by umbrella sampling. The free energy barrier for H 3 O + permeation was consistent with the proton transfer rate deduced from the flagellar rotational speed and number of protons per rotation, which suggests that the gating is the rate-limiting step. Structure and dynamics of the MotA/B with nonprotonated and protonated Asp32, Val43Met, and Val43Leu mutants in MotB were investigated using molecular dynamics simulation. A narrowing of the channel was observed in the mutants, which is consistent with the size-dependent ion selectivity. In MotA/B with the nonprotonated Asp32, the A3 segment in MotA maintained a kink whereas the protonation induced a straighter shape. Assuming that the cytoplasmic domain not included in the atomic model moves as a rigid body, the protonation/deprotonation of Asp32 is inferred to induce a ratchet motion of the cytoplasmic domain, which may be correlated to the motion of the flagellar rotor.proton transfer | bacterial flagellar motor | channel gating | ratchet motion | molecular dynamics B acterial flagella are multifuel engines that convert ion motive force to molecular motor rotation. Escherichia coli has a few proton-driven flagellar motors with stators (protein MotA/B complex) in the inner membrane that act as proton channels (1-5). In addition, Vibrio alginolyticus has a polar flagellum powered by sodium ions (6). Bacillus alcalophilus has motors driven by rubidium (Rb + ), potassium (K + ), and sodium ions (Na + ) that can be converted to Na + -driven motors by a single mutation (7).The proton transfer mechanism in membrane proteins is associated with water wire and/or a hydrogen bond chain (HBC) (8, 9). The water wire comprises water molecules aligned in a protein channel, where protons are transferred by hopping along the wire. Protons are conducted through the hydrogen bonds formed by the polar amino acid residues and water molecules along the proton transfer pathway in the HBC. Protons can also be transferred by diffusion of hydronium ions (H 3 O + ). The diffusion distance in a hydrophilic environment is short in a liquid (the lifetime in water is ca. 1 ps) (10, 11), but it should be longer in a more hydrophobic environment. H 3 O + forms a hydrogen bond (H bond) with the nearest neighbor water molecules and the carbonyl groups, and proton hopping along the H bonds is faster than diffusion of Na ...

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Membrane Topology of the MotA Protein ofEscherichia coil

Cited by 123 publications

References 0 publications

Functional Reconstitution of the Na+-driven Polar Flagellar Motor Component of Vibrio alginolyticus

Functional Reconstitution of the Na+-driven Polar Flagellar Motor Component of Vibrio alginolyticus

Putative channel components for the fast-rotating sodium-driven flagellar motor of a marine bacterium

Gate-controlled proton diffusion and protonation-induced ratchet motion in the stator of the bacterial flagellar motor

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