Ping pong in the pore

Proteins traversing the nuclear pore complex (NPC) bounce back and forth within the central pore until they are finally expelled, according to Weidong Yang, Jeff Gelles, and Siegfried Musser (Texas A&M University System Health Science Center, College Station, TX).

The group imaged single import complexes (ICs)—importin(s) and cargo—interacting with NPCs. Trajectories of the ICs within the pore indicate rapid, random movement forward and backward.

One transport model proposes an affinity gradient across the pore between ICs and pore components, but the back and forth movements do not support this model. Rather, the data suggest that molecules move randomly within the pore and exit either side. “If the IC enters the pore and reexits the same side,” says Musser, “no net energy went in, so you've lost nothing. But if the IC gets out the other side,...