Aconitase

spinqualitylabelsall models 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. Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Major Facilitator 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 transpoter (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.