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Molecular Chaperones and Protein Folding

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.
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Overview of Protein Sorting and Transport

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Eukaryotic cells have different membrane-bound organelles with distinct protein requirements. The process by which proteins are targeted to a specific organelle is called protein sorting.
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ER is the primary site for the maturation and folding of soluble and transmembrane secretory proteins. The calnexin cycle is a specific chaperone system that folds and assesses the confirmation of N-glycosylated proteins before they can exit the ER lumen. The primary players of this quality check pipeline are the lectins, ER-resident chaperones, and a glucosyl transferase enzyme. In case the calnexin system in the lumen fails to salvage a misfolded protein, it is transported to the cytoplasm...

The Unfolded Protein Response

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After folding, the ER assesses the quality of secretory and membrane proteins. The correctly folded proteins are cleared by the calnexin cycle for transport to their final destination, while misfolded proteins are held back in the ER lumen. The ER chaperones attempt to unfold and refold the misfolded proteins but sometimes fail to achieve the correct native conformation. Such terminally misfolded proteins are then exported to the cytosol by ER-associated degradation or ERAD pathway for...

Molecular Chaperones and Protein Folding

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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.
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Related Experiment Video

Updated: May 13, 2026

4D Imaging of Protein Aggregation in Live Cells

4D Imaging of Protein Aggregation in Live Cells

Published on: April 5, 2013

Misfolded proteins partition between two distinct quality control compartments.

Daniel Kaganovich¹, Ron Kopito, Judith Frydman

¹Department of Biology and BioX Program, Stanford University, Stanford, California 94305, USA.

|August 30, 2008

Summary

Misfolded proteins causing neurodegenerative diseases like Huntington's and prion disease accumulate in specific cellular compartments. Their location depends on ubiquitination and aggregation, offering insights into disease mechanisms.

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Related Experiment Videos

Last Updated: May 13, 2026

4D Imaging of Protein Aggregation in Live Cells

4D Imaging of Protein Aggregation in Live Cells

Published on: April 5, 2013

Assays for the Degradation of Misfolded Proteins in Cells

Assays for the Degradation of Misfolded Proteins in Cells

Published on: August 28, 2016

Reconstitution of Msp1 Extraction Activity with Fully Purified Components

Reconstitution of Msp1 Extraction Activity with Fully Purified Components

Published on: August 10, 2021

Area of Science:

Cell Biology
Neuroscience
Biochemistry

Background:

Misfolded protein accumulation in intracellular amyloid inclusions is characteristic of neurodegenerative disorders.
This accumulation is believed to result from failures in cellular protein quality control mechanisms.

Purpose of the Study:

To investigate the formation of misfolded protein inclusions in the eukaryotic cytosol.
To identify intracellular compartments involved in the sequestration of misfolded cytosolic proteins.

Main Methods:

Utilized yeast and mammalian cell culture models.
Examined the role of ubiquitination status and aggregation state in protein partitioning.
Investigated the localization of disease-associated proteins like Huntingtin and prion proteins.

Main Results:

Identified two distinct intracellular compartments for misfolded protein sequestration: a juxtanuclear compartment and a perivacuolar inclusion.
Protein partitioning depends on ubiquitination and aggregation state.
Soluble, ubiquitinated proteins target the juxtanuclear compartment, while aggregated proteins go to the perivacuolar compartment.
Disease-associated Huntingtin and prion proteins preferentially accumulate in the perivacuolar compartment.

Conclusions:

Established a framework for understanding the compartmentalization of misfolded proteins in the cytosol.
Demonstrated that enhancing ubiquitination can redirect misfolded proteins to the juxtanuclear compartment.
Provided insights into the preferential accumulation of amyloidogenic proteins in disease-associated inclusions.