9r9o

Structural highlights

Function

SSB1_YEAST Ribosome-bound, Hsp70-type chaperone that assists in the cotranslational folding of newly synthesized proteins in the cytosol. Stimulates folding by interacting with nascent chains, binding to short, largely hydrophobic sequences exposed by unfolded proteins, thereby stabilizing longer, more slowly translated, and aggregation-prone nascent polypeptides and domains that cannot fold stably until fully synthesized. The Hsp70-protein substrate interaction depends on ATP-binding and on allosteric regulation between the NBD and the SBD. The ATP-bound state is characterized by a fast exchange rate of substrate (low affinity state), while in the ADP-bound state exchange is much slower (high affinity state). During the Hsp70 cycle, the chaperone switches between the ATP-bound state (open conformation) and the ADP-bound state (closed conformation) by major conformational rearrangements involving mainly the lid domain. Ssb cooperates with a specific Hsp40/Hsp70 co-chaperone termed the ribosome-associated complex (RAC), which stimulates the ATPase activity of the ribosome-associated pool of Ssbs and switches it to the high affinity substrate binding state. Hsp110 chaperone SSE1 and FES1 act as nucleotide exchange factors that cause substrate release.^{[1] [2] [3] [4] [5] [6] [7] [8]}

References

1. ↑ Pfund C, Huang P, Lopez-Hoyo N, Craig EA. Divergent functional properties of the ribosome-associated molecular chaperone Ssb compared with other Hsp70s. Mol Biol Cell. 2001 Dec;12(12):3773-82. PMID:11739779 doi:10.1091/mbc.12.12.3773
2. ↑ Gautschi M, Mun A, Ross S, Rospert S. A functional chaperone triad on the yeast ribosome. Proc Natl Acad Sci U S A. 2002 Apr 2;99(7):4209-14. PMID:11929994 doi:10.1073/pnas.062048599
3. ↑ Nelson RJ, Ziegelhoffer T, Nicolet C, Werner-Washburne M, Craig EA. The translation machinery and 70 kd heat shock protein cooperate in protein synthesis. Cell. 1992 Oct 2;71(1):97-105. PMID:1394434
4. ↑ Yam AY, Albanèse V, Lin HT, Frydman J. Hsp110 cooperates with different cytosolic HSP70 systems in a pathway for de novo folding. J Biol Chem. 2005 Dec 16;280(50):41252-61. PMID:16219770 doi:10.1074/jbc.M503615200
5. ↑ Shaner L, Wegele H, Buchner J, Morano KA. The yeast Hsp110 Sse1 functionally interacts with the Hsp70 chaperones Ssa and Ssb. J Biol Chem. 2005 Dec 16;280(50):41262-9. PMID:16221677 doi:10.1074/jbc.M503614200
6. ↑ Willmund F, del Alamo M, Pechmann S, Chen T, Albanèse V, Dammer EB, Peng J, Frydman J. The cotranslational function of ribosome-associated Hsp70 in eukaryotic protein homeostasis. Cell. 2013 Jan 17;152(1-2):196-209. PMID:23332755 doi:10.1016/j.cell.2012.12.001
7. ↑ James P, Pfund C, Craig EA. Functional specificity among Hsp70 molecular chaperones. Science. 1997 Jan 17;275(5298):387-9. PMID:8994035 doi:10.1126/science.275.5298.387
8. ↑ Pfund C, Lopez-Hoyo N, Ziegelhoffer T, Schilke BA, Lopez-Buesa P, Walter WA, Wiedmann M, Craig EA. The molecular chaperone Ssb from Saccharomyces cerevisiae is a component of the ribosome-nascent chain complex. EMBO J. 1998 Jul 15;17(14):3981-9. PMID:9670014 doi:10.1093/emboj/17.14.3981