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Related Concept Videos

Molecular Chaperones and Protein Folding03:00

Molecular Chaperones and Protein Folding

The native conformation of a protein is formed by interactions between the side chains of its constituent amino acids. When the amino acids cannot form these interactions, the protein cannot fold by itself and needs chaperones. Notably, chaperones do not relay any additional information required for the folding of polypeptides; the native conformation of a protein is determined solely by its amino acid sequence. Chaperones catalyze protein folding without being a part of the folded protein.
The...
Molecular Chaperones and Protein Folding03:00

Molecular Chaperones and Protein Folding

The native conformation of a protein is formed by interactions between the side chains of its constituent amino acids. When the amino acids cannot form these interactions, the protein cannot fold by itself and needs chaperones. Notably, chaperones do not relay any additional information required for the folding of polypeptides; the native conformation of a protein is determined solely by its amino acid sequence. Chaperones catalyze protein folding without being a part of the folded protein.
The...
Bacterial Protein Maturation01:26

Bacterial Protein Maturation

Bacterial protein maturation is a tightly regulated process that ensures newly synthesized polypeptides achieve correct functional conformations. This maturation involves a series of modifications, folding events, and quality control steps, often assisted by specialized chaperone proteins.N-Terminal ModificationsThe maturation of bacterial polypeptides begins cotranslationally as the polypeptide exits the ribosome. The first amino acid, N-formylmethionine (fMet), is typically modified at the...
Cotranslational Protein Translocation01:20

Cotranslational Protein Translocation

Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the translocation machinery are still conserved between prokaryotes and eukaryotes.
Sec61 channel partners for cotranslational translocation
During cotranslational translocation, the Sec61 channel partners with the signal recognition particle (SRP), the signal recognition particle receptor (SR), and the ribosomes to transport the nascent polypeptide chain...
Directing Proteins to the Rough Endoplasmic Reticulum01:34

Directing Proteins to the Rough Endoplasmic Reticulum

The organelle-specific signaling sequences direct proteins synthesized in the cytosol to their final destination like ER, mitochondria, peroxisomes, etc. Some of the proteins directed to ER are then trafficked via vesicles to other organelles within the cell or the extracellular environment through the Golgi complex. For example, the rough ER synthesizes soluble proteins for transportation to the lysosomes or secretion out of the cell. It can also synthesize transmembrane proteins that can...
Protein Translocation Machinery on the ER Membrane01:28

Protein Translocation Machinery on the ER Membrane

The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
Sec61 protein conducting channel
In eukaryotes, the translocon complex comprises a core heterotrimeric translocator channel called the Sec61 complex. This channel includes three transmembrane proteins, Sec61α, Sec61β, and Sec61γ, and is the largest subunit of the translocon complex.

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In Situ Monitoring of Transiently Formed Molecular Chaperone Assemblies in Bacteria, Yeast, and Human Cells
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The chaperone network connected to human ribosome-associated complex.

Himjyot Jaiswal1, Charlotte Conz, Hendrik Otto

  • 1Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Str. 17, D-79104 Freiburg, Germany.

Molecular and Cellular Biology
|January 20, 2011
PubMed
Summary

Mammalian ribosome-associated complex (mRAC) partially complements yeast RAC function. However, human Hsp70 homologs do not substitute for yeast Ssb, indicating distinct chaperone-ribosome interactions in mammals.

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Area of Science:

  • Molecular Biology
  • Cell Biology
  • Protein Biochemistry

Background:

  • The ribosome-associated complex (RAC) in yeast (Saccharomyces cerevisiae) interacts with the Hsp70 homolog Ssb.
  • Mammalian cells possess a homologous complex, mRAC, comprising MPP11 and Hsp70L1.
  • Understanding the functional conservation and differences between yeast RAC and mRAC is crucial for elucidating chaperone-assisted protein biogenesis.

Purpose of the Study:

  • To investigate the functional conservation between yeast RAC and mammalian mRAC.
  • To determine if human Hsp70 homologs can functionally replace yeast Ssb.
  • To elucidate the mechanistic basis of mRAC's interaction with Hsp70.

Main Methods:

  • Depletion of mRAC in HeLa cells to assess growth defects.
  • Complementation assays using human Hsp70 homologs in yeast strains lacking Ssb.
  • Analysis of Hsp70-homolog binding to ribosomes.
  • Investigating the role of ATP binding and hydrolysis by Hsp70L1 in mRAC function.

Main Results:

  • Depletion of mRAC in HeLa cells caused growth defects similar to yeast lacking RAC.
  • Human Hsp70 homologs failed to complement yeast Ssb-deficient strains or bind ribosomes similarly to Ssb.
  • mRAC specifically partnered with human Hsp70, not Hsc70.
  • ATP binding, but not hydrolysis, by Hsp70L1 influenced mRAC's function with Hsp70.

Conclusions:

  • Mammalian mRAC and yeast RAC share functional conservation in assisting ribosome function.
  • Despite functional conservation, yeast and mammalian cells utilize distinct Hsp70-type chaperones and interaction mechanisms.
  • The findings highlight divergent evolutionary strategies for chaperone-assisted polypeptide synthesis in eukaryotes.