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Aconitase

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GplT from E. coli is a Major Facilitator antiporter, rocker-switch type. We use it as example but the principle remains the same for all other Major Facilitators.

Drag the structure with the mouse to rotate

Major Facilitators are membrane proteins that help with both influx and outflux of specific small molecules. They are neither passive channels, nor do they active pumping, like the ATPases. Like a rocker-switch, they tilt between the two states 'outside open' and 'inside open'. This tilting (or switching) is triggered when a molecule has docked inside, and it transports the molecule to the other side. We call these transporters antiporter because, when switching back, usually a second, different, molecule is transported in the opposite direction. Have a look at the complete process involving all molecules.

As example above, we used the glucose-3-phosphate transporter (GlpT) from E. coli. The glpT subfamily of transporters consist of several transport proteins from bacteria like E. coli and Salmonella typhimurium, but also the human glucose-6-phosphate translocase. They all are evolutionary connected and have 12 transmembrane helices that stand together to make an opening between them, not unlike a channel. This channel, however, is unpassable as long as not the right molecule (glucose-3-phosphate in the case of GlpT) is docked into it.[1][2][3]

References

  1. ↑ Law CJ, Maloney PC, Wang DN. Ins and outs of major facilitator superfamily antiporters. Annu Rev Microbiol. 2008;62:289-305. PMID:18537473 doi:http://dx.doi.org/10.1146/annurev.micro.61.080706.093329
  2. ↑ Law CJ, Yang Q, Soudant C, Maloney PC, Wang DN. Kinetic evidence is consistent with the rocker-switch mechanism of membrane transport by GlpT. Biochemistry. 2007 Oct 30;46(43):12190-7. Epub 2007 Oct 4. PMID:17915951 doi:http://dx.doi.org/10.1021/bi701383g
  3. ↑ Huang Y, Lemieux MJ, Song J, Auer M, Wang DN. Structure and mechanism of the glycerol-3-phosphate transporter from Escherichia coli. Science. 2003 Aug 1;301(5633):616-20. PMID:12893936 doi:10.1126/science.1087619
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