title: Flexible phenylalanine-glycine nucleoporins as entropic barriers to nucleocytoplasmic transport.
abstract: Natively unfolded phenylalanine-glycine (FG)-repeat domains are alleged to form the physical constituents of the selective barrier-gate in nuclear pore complexes during nucleocytoplasmic transport. Presently, the biophysical mechanism behind the selective gate remains speculative because of a lack of information regarding the nanomechanical properties of the FG domains. In this work, we have applied the atomic force microscope to measure the mechanical response of individual and clusters of FG molecules. Single-molecule force spectroscopy reveals that FG molecules are unfolded and highly flexible. To provide insight into the selective gating mechanism, an experimental platform has been constructed to study the collective behavior of surface-tethered FG molecules at the nanoscale. Measurements indicate that the collective behavior of such FG molecules gives rise to an exponentially decaying long-range steric repulsive force. This finding indicates that the molecules are thermally mobile in an extended polymer brush-like conformation. This assertion is confirmed by observing that the brush-like conformation undergoes a reversible collapse transition in less polar solvent conditions. These findings reveal how FG-repeat domains may simultaneously function as an entropic barrier and a selective trap in the near-field interaction zone of nuclear pore complexes; i.e., selective gate.
authors.affiliation: M. E. Müller Institute for Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland.
authors.forename: Roderick Y H
authors.initials: RY
authors.lastname: Lim
authors.forename: Ning-Ping
authors.initials: NP
authors.lastname: Huang
authors.forename: Joachim
authors.initials: J
authors.lastname: Köser
authors.forename: Jie
authors.initials: J
authors.lastname: Deng
authors.forename: K H Aaron
authors.initials: KH
authors.lastname: Lau
authors.forename: Kyrill
authors.initials: K
authors.lastname: Schwarz-Herion
authors.forename: Birthe
authors.initials: B
authors.lastname: Fahrenkrog
authors.forename: Ueli
authors.initials: U
authors.lastname: Aebi
mesh_terms: D021581:Active Transport, Cell Nucleus; D004151:Dipeptides / Q000235:genetics / Q000378:metabolism*; D019277:Entropy; D006046:Gold / Q000737:chemistry; D006801:Humans; D018625:Microscopy, Atomic Force; D049329:Nanostructures / Q000737:chemistry / Q000648:ultrastructure; D028861:Nuclear Pore Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D018583:Pliability
chemical_list: D004151:Dipeptides; D028861:Nuclear Pore Complex Proteins; C029660:glycylphenylalanine; D006046:Gold