Motility protein A

{{Use dmy dates|date=April 2022}}

{{Infobox nonhuman protein

| Name = Motility protein A

| image =

| width =

| caption =

| Organism = Escherichia coli str. K-12

| TaxID = 511145

| Symbol = motA

| AltSymbols = ECK1891; flaJ; JW1879

| EntrezGene = 947564

| HGNCid =

| OMIM =

| PDB =

| RefSeqmRNA =

| RefSeqProtein = NP_416404.1

| UniProt = P09348

| ECnumber =

| Chromosome = chromosome

| EntrezChromosome = NC_000913

| GenLoc_start = 1974142

| GenLoc_end = 1975295

}}

Motility protein A (MotA), is a bacterial protein that is encoded by the motA gene. It is a component of the flagellar motor.{{cite journal |vauthors=Blair DF, Berg HC | title = The MotA protein of E. coli is a proton-conducting component of the flagellar motor | journal = Cell | volume = 60 | issue = 3 | pages = 439–49 |date=February 1990 | pmid = 2154333 | doi = 10.1016/0092-8674(90)90595-6| s2cid = 10593013 }} More specifically, MotA and MotB make the stator of a H⁺ driven bacterial flagella and surround the rotor as a ring of about 8–10 particles. MotA and MotB are integral membrane proteins.{{cite journal |vauthors=Stolz B, Berg HC | title = Evidence for interactions between MotA and MotB, torque-generating elements of the flagellar motor of Escherichia coli | journal = J. Bacteriol. | volume = 173 | issue = 21 | pages = 7033–7 |date=November 1991 | doi = 10.1128/jb.173.21.7033-7037.1991 | pmid = 1938906 | pmc = 209062 }} MotA has four transmembrane domains.

Both proteins are part of the H⁺ channel that makes possible the flux of protons and the motor's rotation.

In MotA mutants, the motor function is re-established if the MotA protein is expressed.

Though MotA and MotB are part of the proteins required for H⁺ mediated flagellar motility, they show a high degree of homology to the PomA and PomB proteins present in bacterial species utilizing Na⁺ ion fluxes to power flagella and studies have revealed that a 'pomA' mutant of Vibrio alginolyticus can regain motility by expression of MotA.{{cite journal |vauthors=Asai Y, Kawagishi I, Sockett RE, Homma M | title = Hybrid motor with H(+)- and Na(+)-driven components can rotate Vibrio polar flagella by using sodium ions | journal = J. Bacteriol. | volume = 181 | issue = 20 | pages = 6332–8 |date=October 1999 | doi = 10.1128/JB.181.20.6332-6338.1999 | pmid = 10515922 | pmc = 103767 }} As restoring motility of pomA mutants by heterologous expression of MotA does not change the ion used to power the flagellum of the transgenic Vibrio alginolyticus, MotA is not in itself an essential specificity factor in ion selectivity, though that does not exclude it being partially involved in determining ion specificity of the flagellar complex.