Structural basis for regulation of the nucleo-cytoplasmic distribution of Bag6 by TRC35
The metazoan protein BCL2-associated athanogene cochaperone 6 (Bag6) forms a hetero-trimeric complex with ubiquitin-like 4A and transmembrane domain recognition complex 35 (TRC35). This Bag6 complex is involved in tail-anchored protein targeting and various protein quality-control pathways in the cytosol as well as regulating transcription and histone methylation in the nucleus. Here we present a crystal structure of Bag6 and its cytoplasmic retention factor TRC35, revealing that TRC35 is remarkably conserved throughout the opisthokont lineage except at the C-terminal Bag6-binding groove, which evolved to accommodate Bag6, a unique metazoan factor. While TRC35 and its fungal homolog, guided entry of tail-anchored protein 4 (Get4), utilize a conserved hydrophobic patch to bind their respective partners, Bag6 wraps around TRC35 on the opposite face relative to the Get4–5 interface. We further demonstrate that TRC35 binding is critical not only for occluding the Bag6 nuclear localization sequence from karyopherin α to retain Bag6 in the cytosol but also for preventing TRC35 from succumbing to RNF126-mediated ubiquitylation and degradation. The results provide a mechanism for regulation of Bag6 nuclear localization and the functional integrity of the Bag6 complex in the cytosol.
© 2017 National Academy of Sciences. Edited by Jeffrey L. Brodsky, University of Pittsburgh, Pittsburgh, PA, and accepted by Editorial Board Member F. Ulrich Hartl, September 20, 2017 (received for review February 23, 2017). Published online before print October 17, 2017. We thank Daniel Lin and Jens Kaiser for help with data processing, Catherine Day for technical support, members of the W.M.C. laboratory for support and useful discussions, Gordon and Betty Moore for support of the Molecular Observatory at California Institute of Technology, and the staff at the Stanford Synchrotron Radiation Lightsource for assistance with synchrotron data collection. W.M.C. is supported by NIH Grant R01GM097572. Author contributions: J.-Y.M., Y.Y., and W.M.C. designed research; J.-Y.M., Y.X., and Y.Y. performed research; J.-Y.M., Y.X., and Y.Y. contributed new reagents/analytic tools; J.-Y.M., Y.Y., and W.M.C. analyzed data; and J.-Y.M. and W.M.C. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. J.L.B. is a guest editor invited by the Editorial Board. Data deposition: The atomic coordinates and structure factors reported in this paper have been deposited in the Protein Data Bank (PDB), https://www.wwpdb.org (PDB ID code 6AU8). This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1702940114/-/DCSupplemental. Published under the PNAS license.
Submitted - 154351.full.pdf
Published - PNAS-2017-Mock-11679-84.pdf
Supplemental Material - pnas.201702940SI.pdf