biostudies-literatureSolmaz SRNIBIB NIH HHSHoward Hughes Medical Institute5858-63https://www.ebi.ac.uk/biostudies/studies/S-EPMC3625290biostudies-literatureUnknown110(15)We recently showed that the three "channel" nucleoporins, Nup54, Nup58, and Nup62, interact with each other through only four distinct sites and established the crystal structures of the two resulting "interactomes," Nup54•Nup58 and Nup54•Nup62. We also reported instability of the Nup54•Nup58 interactome and previously determined the atomic structure of the relevant Nup58 segment by itself, demonstrating that it forms a twofold symmetric tetramer. Here, we report the crystal structure of the relevant free Nup54 segment and show that it forms a tetrameric, helical bundle that is structurally "conditioned" for instability by a central patch of polar hydrogen-bonded residues. Integrating these data with our previously reported results, we propose a "ring cycle" for dilating and constricting tProceedings of the National Academy of Sciences of the United States of AmericaRing cycle for dilating and constricting the nuclear pore.PMC3625290P30 EB009998Blobel GSolmaz SRMelcak IfalseRing cycle for dilating and constricting the nuclear pore.We recently showed that the three "channel" nucleoporins, Nup54, Nup58, and Nup62, interact with each other through only four distinct sites and established the crystal structures of the two resulting "interactomes," Nup54•Nup58 and Nup54•Nup62. We also reported instability of the Nup54•Nup58 interactome and previously determined the atomic structure of the relevant Nup58 segment by itself, demonstrating that it forms a twofold symmetric tetramer. Here, we report the crystal structure of the relevant free Nup54 segment and show that it forms a tetrameric, helical bundle that is structurally "conditioned" for instability by a central patch of polar hydrogen-bonded residues. Integrating these data with our previously reported results, we propose a "ring cycle" for dilating and constricting t2013-01-01T00:00:00Z2013 Apr2025-04-03T22:18:45.862Z2019-03-27T01:07:22ZS-EPMC36252902347965110.1073/pnas.1302655110