Coupling of ribosomal translation with cotranslational protein folding is essential for cellular homeostasis. In eukaryotes, Hsp70 and its J-domain cochaperone, the heterodimeric ribosome-associated complex (RAC), are central to this process; however, mechanistic insights into the coordination of Hsp70 function with translation remain limited. Here, we present two cryo-EM structures of the ribosome-bound yeast Hsp70 Ssb, identifying Rpl25/uL23 as the ribosomal binding site and revealing its interaction with a model nascent chain. Together with detailed biochemical and mutational analyses, these structures enable us to delineate the intricate RAC-dependent cycle, which positions the substrate binding domain of Ssb-ATP close to the tunnel exit to receive nascent chains. This arrangement allows Ssb to undergo substantial conformational changes upon ATP hydrolysis without steric clashes with the ribosome, while the substrate binding domain of Ssb, now anchored by the tightly bound nascent chain, remains close to the tunnel exit.
Organizational Affiliation:
Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
Research Institute of Molecular Pathology (IMP), Campus Vienna Biocenter 1, Vienna, Austria.
Vienna BioCenter PhD Program, Doctoral School of the University of Vienna and Medical University of Vienna, Vienna, Austria.
Institute of Physical Chemistry, University of Freiburg, Freiburg, Germany.
Spemann Graduate School of Biology and Medicine (SGBM), University of Freiburg, Freiburg, Germany.
BIOSS Centre for Biological Signalling Studies, and CIBSS Centre for Integrative Biological Signalling Studies, University of Freiburg, Freiburg, Germany.
Research Institute of Molecular Pathology (IMP), Campus Vienna Biocenter 1, Vienna, Austria. david.haselbach@imp.ac.at.
Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany. sabine.rospert@biochemie.uni-freiburg.de.
BIOSS Centre for Biological Signalling Studies, and CIBSS Centre for Integrative Biological Signalling Studies, University of Freiburg, Freiburg, Germany. sabine.rospert@biochemie.uni-freiburg.de.
Download Mendeley
