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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:P09348
Protein Name:Chemotaxis protein MotA aka B1890
Length:295
Molecular Weight:32011.00
Species:Escherichia coli [83333]
Number of TMSs:4
Location1 / Topology2 / Orientation3: Cell inner membrane1 / Multi-pass membrane protein2
Substrate hydron, proton

Cross database links:

DIP: DIP-10244N
RefSeq: AP_002510.1    NP_416404.1   
Entrez Gene ID: 947564   
Pfam: PF01618   
BioCyc: EcoCyc:MOTA-FLAGELLAR-MOTOR-STATOR-PROTEIN    ECOL168927:B1890-MONOMER   
KEGG: ecj:JW1879    eco:b1890   

Gene Ontology

GO:0016021 C:integral to membrane
GO:0005886 C:plasma membrane
GO:0003774 F:motor activity
GO:0008565 F:protein transporter activity
GO:0006935 P:chemotaxis
GO:0001539 P:ciliary or flagellar motility
GO:0015992 P:proton transport

References (8)

[1] “Gene sequence and predicted amino acid sequence of the motA protein, a membrane-associated protein required for flagellar rotation in Escherichia coli.”  Dean G.E.et.al.   6090403
[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] “Nucleotide sequence of the Escherichia coli motB gene and site-limited incorporation of its product into the cytoplasmic membrane.”  Stader J.et.al.   3007435
[6] “Mutations in the MotA protein of Escherichia coli reveal domains critical for proton conduction.”  Blair D.F.et.al.   1719217
[7] “Membrane topology of the MotA protein of Escherichia coli.”  Zhou J.et.al.   7643400
[8] “Global topology analysis of the Escherichia coli inner membrane proteome.”  Daley D.O.et.al.   15919996

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FASTA formatted sequence
1:	MLILLGYLVV LGTVFGGYLM TGGSLGALYQ PAELVIIAGA GIGSFIVGNN GKAIKGTLKA 
61:	LPLLFRRSKY TKAMYMDLLA LLYRLMAKSR QMGMFSLERD IENPRESEIF ASYPRILADS 
121:	VMLDFIVDYL RLIISGHMNT FEIEALMDEE IETHESEAEV PANSLALVGD SLPAFGIVAA 
181:	VMGVVHALGS ADRPAAELGA LIAHAMVGTF LGILLAYGFI SPLATVLRQK SAETSKMMQC 
241:	VKVTLLSNLN GYAPPIAVEF GRKTLYSSER PSFIELEEHV RAVKNPQQQT TTEEA