Structural basis for regulation of the nucleo-cytoplasmic distribution of Bag6 by TRC35

Proc Natl Acad Sci U S A. 2017 Oct 31;114(44):11679-11684. doi: 10.1073/pnas.1702940114. Epub 2017 Oct 17.


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.

Keywords: GET pathway; X-ray crystallography; proteasome-dependent degradation; tail-anchor recognition complex; tail-anchor targeting.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cloning, Molecular
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Gene Expression Regulation / physiology
  • HEK293 Cells
  • Humans
  • Molecular Chaperones / chemistry*
  • Molecular Chaperones / metabolism
  • Mutation
  • Phylogeny
  • Protein Binding
  • Protein Domains
  • Protein Transport / physiology*
  • Two-Hybrid System Techniques
  • Ubiquitin-Protein Ligases / metabolism
  • Ubiquitination
  • alpha Karyopherins / chemistry
  • alpha Karyopherins / metabolism


  • BAG6 protein, human
  • Molecular Chaperones
  • Trc35 protein, human
  • alpha Karyopherins
  • RNF126 protein, human
  • Ubiquitin-Protein Ligases

Associated data

  • PDB/6AU8