Structural inventory of cotranslational protein folding by the eukaryotic RAC complex

Nat Struct Mol Biol. 2023 May;30(5):670-677. doi: 10.1038/s41594-023-00973-1. Epub 2023 Apr 20.

Abstract

The challenge of nascent chain folding at the ribosome is met by the conserved ribosome-associated complex (RAC), which forms a chaperone triad with the Hsp70 protein Ssb in fungi, and consists of the non-canonical Hsp70 Ssz1 and the J domain protein Zuotin (Zuo1). Here we determine cryo-EM structures of Chaetomium thermophilum RAC bound to 80S ribosomes. RAC adopts two distinct conformations accommodating continuous ribosomal rotation by a flexible lever arm. It is held together by a tight interaction between the Ssz1 substrate-binding domain and the Zuo1 N terminus, and additional contacts between the Ssz1 nucleotide-binding domain and Zuo1 J- and Zuo1 homology domains, which form a rigid unit. The Zuo1 HPD motif conserved in J-proteins is masked in a non-canonical interaction by the Ssz1 nucleotide-binding domain, and allows the positioning of Ssb for activation by Zuo1. Overall, we provide the basis for understanding how RAC cooperates with Ssb in a dynamic nascent chain interaction and protein folding.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • HSP70 Heat-Shock Proteins / chemistry
  • Molecular Chaperones / metabolism
  • Nucleotides / metabolism
  • Protein Binding
  • Protein Folding
  • Ribosomes / metabolism
  • Saccharomyces cerevisiae Proteins* / metabolism
  • Saccharomyces cerevisiae* / metabolism

Substances

  • Saccharomyces cerevisiae Proteins
  • HSP70 Heat-Shock Proteins
  • Nucleotides
  • ZUO1 protein, S cerevisiae
  • Molecular Chaperones
  • SSZ1 protein, S cerevisiae