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1.A.30.1.1
The flagellar motor (pmf-dependent) (MotA-MotB). TMSs 3 and 4 of MotA and the single TMS of MotB comprise the proton channel, which is inactive until the complex assembles into a motor. Hosking et al. 2006 identify a periplasmic segment of the MotB protein that acts as a plug to prevent premature proton flow. The plug is in the periplasm just C-terminal to the MotB TMS flanked by Pro52 and Pro65. The Pro residues and Ile58, Tyr61, and Phe62 are essential for plug function (Hosking et al. 2006). The mechanism of proton passage and coupling to flagellar rotation has been proposed (Nishihara and Kitao 2015).  About a dozen MotA/B complexes are anchored to the peptidoglycan layer around the motor through the C-terminal peptidoglycan-binding domain of MotB (Castillo et al. 2013). Dynamic permeation by hydronium ions, sodium ions, and water molecules has been observed using steered molecular dynamics simulations, and free energy profiles for ion/water permeation were calculated (Kitao and Nishihara 2017). They also examined the possible ratchet motion of the cytoplasmic domain induced by the protonation/deprotonation cycle of the MotB proton binding site, Asp32. The motor (MotAB) consists of a dynamic population of mechanosensitive stators that are embedded in the inner membrane and activate in response to external load. This entails assembly around the rotor, anchoring to the peptidoglycan layer to counteract torque from the rotor and opening of a cation channel to facilitate an influx of cations, which is converted into mechanical rotation. Stator complexes are comprised of four copies of an integral membrane A subunit and two copies of a B subunit. Each B subunit includes a C-terminal OmpA-like peptidoglycan-binding (PGB) domain. This is thought to be linked to a single N-terminal transmembrane helix by a long unstructured peptide, which allows the PGB domain to bind to the peptidoglycan layer during stator anchoring. The high-resolution crystal structures of flagellar motor PGB domains from Salmonella enterica have been solved (Liew et al. 2017). Change in the C ring conformation for switching and rotation involve loose and tight intersubunit interactions (Sakai et al. 2019).

Accession Number:P0AF06
Protein Name:Chemotaxis protein MotB aka B1889
Length:308
Molecular Weight:34186.00
Species:Escherichia coli [83333]
Number of TMSs:1
Location1 / Topology2 / Orientation3: Cell inner membrane1 / Single-pass type II membrane protein2
Substrate hydron, proton

Cross database links:

DIP: DIP-47996N
RefSeq: AP_002509.1    NP_416403.1   
Entrez Gene ID: 946402   
Pfam: PF00691   
BioCyc: EcoCyc:MOTB-FLAGELLAR-MOTOR-STATOR-PROTEIN    ECOL168927:B1889-MONOMER   
KEGG: ecj:JW1878    eco:b1889   

Gene Ontology

GO:0009279 C:cell outer membrane
GO:0016021 C:integral to membrane
GO:0005886 C:plasma membrane
GO:0006935 P:chemotaxis
GO:0001539 P:ciliary or flagellar motility

References (7)

[1] “Nucleotide sequence of the Escherichia coli motB gene and site-limited incorporation of its product into the cytoplasmic membrane.”  Stader J.et.al.   3007435
[2] “A 460-kb DNA sequence of the Escherichia coli K-12 genome corresponding to the 40.1-50.0 min region on the linkage map.”  Itoh T.et.al.   9097040
[3] “The complete genome sequence of Escherichia coli K-12.”  Blattner F.R.et.al.   9278503
[4] “Highly accurate genome sequences of Escherichia coli K-12 strains MG1655 and W3110.”  Hayashi K.et.al.   16738553
[5] “Tandem translation starts in the cheA locus of Escherichia coli.”  Kofoid E.C.et.al.   2002011
[6] “Bacterial motility: membrane topology of the Escherichia coli MotB protein.”  Chun S.Y.et.al.   2447650
[7] “Mutant MotB proteins in Escherichia coli.”  Blair D.F.et.al.   2061285

External Searches:

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Predict TMSs (Predict number of transmembrane segments)
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FASTA formatted sequence
1:	MKNQAHPIIV VKRRKAKSHG AAHGSWKIAY ADFMTAMMAF FLVMWLISIS SPKELIQIAE 
61:	YFRTPLATAV TGGDRISNSE SPIPGGGDDY TQSQGEVNKQ PNIEELKKRM EQSRLRKLRG 
121:	DLDQLIESDP KLRALRPHLK IDLVQEGLRI QIIDSQNRPM FRTGSADVEP YMRDILRAIA 
181:	PVLNGIPNRI SLSGHTDDFP YASGEKGYSN WELSADRANA SRRELMVGGL DSGKVLRVVG 
241:	MAATMRLSDR GPDDAVNRRI SLLVLNKQAE QAILHENAES QNEPVSALEK PEVAPQVSVP 
301:	TMPSAEPR