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The Nup62 Coiled-Coil Motif Provides Plasticity for Triple-Helix Bundle Formation

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journal contribution
posted on 13.04.2017, 00:00 by Pravin S. Dewangan, Parshuram J. Sonawane, Ankita R. Chouksey, Radha Chauhan
The central transport channel of the vertebrate nuclear pore complex (NPC) consists of nucleoporins: Nup62, Nup54, and Nup58. The coiled-coil domains in α-helical regions of these nucleoporins are thought to be crucial for several protein–protein interactions in the NPC subcomplexes. In this study, we determined the crystal structure of the coiled-coil domain of rat Nup62 fragment (residues 362–425) to 2.4 Å resolution. The crystal structure shows the conserved coiled-coil domain as a parallel three-helix bundle for the Nup62­(362–425) fragment. On the basis of our size exclusion chromatography coupled to multiangle light scattering analysis and glutaraldehyde cross-linking experiments, we conclude that the Nup62(362–425) fragment displays dynamic behavior in solution and can also exist in either homodimeric or homotrimeric states. Our comparative analysis of the rat Nup62(362–425) homotrimeric structure with previously reported heterotrimeric structures [rat Nup62(362–425)·Nup54(346–407) and Xenopus Nup62(358–485)·Nup54(315–450)·Nup58(283–406) complexes] demonstrates the structural basis for parallel triple-helix bundle formation for Nup62 with different partners. Moreover, we show that the coiled-coil domain of Nup62 is sufficient for interaction with the coiled-coil domain of rat Exo70, a protein in an exocyst complex. On the basis of these observations, we suggest the plausible chain replacement mechanism that yields to diverse protein assemblies with Nup62. In summary, the coiled-coil motif present in Nup62 imparts the ability to form a homotrimer and heterotrimers either with Nup54 or with Nup54–Nup58 within the NPCs as well as with Exo70 beyond the NPCs. These complexes of Nup62 suggest the crucial role of the coiled-coil motifs in providing plasticity to various modular assemblies.