Entropy guards pore

The rapid fluctuations of flexible FG repeat–containing nucleoporins (FG Nups) form an entropic barrier to would-be entrants into the nuclear pore complex (NPC), according to Roderick Lim (University of Basel, Switzerland) and colleagues.

FG Nups, which consist of large natively unfolded domains, are the pore's gatekeepers—they keep out proteins that are not bound to transport receptors. Thus, says Lim, “the mechanics of transport lies in how FG domains behave at the nanoscale.”

To examine this behavior, the group used atomic force microscopy on clusters of one such FG domain, called cNup153, tethered at one end to gold nanodots. The forces exerted by the cluster just nanometers above the dot were reminiscent of the behavior of a physical phenomenon known as polymer brushes. Specifically, random flexible movements of polymers (or unfolded FG...