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Covalently Linked Protein Regulators

Covalently Linked Protein Regulators

Proteins can undergo many types of post-translational modifications, often in response to changes in their environment. These modifications play an important role in the function and stability of these proteins. Covalently linked molecules include functional groups, such as methyl, acetyl, and phosphate groups, and also small proteins, such as ubiquitin. There are around 200 different types of covalent regulators that have been identified.
These groups modify specific amino acids in a protein.

Regulated Protein Degradation

Regulated Protein Degradation

It is vital to regulate the activity of enzymatic as well as non-enzymatic proteins inside the cell. This can be achieved either through creating a balance between their rate of synthesis and degradation or regulating the intrinsic activity of the protein. Both these regulation mechanisms play an essential role in the normal functioning of cells.
Protein degradation plays two important roles in the cells. It helps to protect cells from misfolded or damaged proteins before they lead to a...

The Proteasome

The Proteasome

Eukaryotic cells can degrade proteins through several pathways. One of the most important among these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. This involves participation of a series of enzymes including— E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3 (ubiquitin...

The Proteasome

The Proteasome

Eukaryotic cells can degrade proteins through several pathways. One of the most important amongst these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. A series of enzymes carry out the ubiquitination of the target proteins - E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...

The Unfolded Protein Response

The Unfolded Protein Response

The ER is the hub of protein synthesis in a cell. It has robust systems to quality control protein folding and also for degradation of terminally misfolded proteins. Under normal conditions, a small proportion of misfolded proteins that cannot be salvaged need to be transported to the cytoplasm by the ER-associated degradation or ERAD pathways. However, if the ERAD cannot handle the misfolded proteins, the cell activates the unfolded protein response or UPR to adjust the protein folding...

Protein Denaturation

Protein Denaturation

The function of proteins depends on their native three-dimensional structure, which is dictated by the amino acid sequence of the specific protein. Folding of the polypeptide chain takes place under specific conditions that energetically favor the folded conformation. In contrast, protein denaturation occurs spontaneously under unfavorable conditions that disrupt the integrity of the folded conformation. Thus, the chemical and physical environment of a protein, such as significant changes in pH...

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Updated: May 21, 2026

Detection of Protein Ubiquitination

Detection of Protein Ubiquitination

Published on: August 19, 2009

Cold-induced changes in the protein ubiquitin.

Min-Kyu Cho¹, Shengqi Xiang, Hai-Young Kim

¹Department for NMR-Based Structural Biology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.

|June 28, 2012

Summary

Ubiquitin remains folded at low temperatures, but hydrogen bonds in its beta-sheet region weaken, potentially initiating cold-denaturation and facilitating protein complex formation.

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Last Updated: May 21, 2026

Detection of Protein Ubiquitination

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Published on: August 19, 2009

4D Imaging of Protein Aggregation in Live Cells

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Published on: April 5, 2013

In Vitro Ubiquitination and Deubiquitination Assays of Nucleosomal Histones

In Vitro Ubiquitination and Deubiquitination Assays of Nucleosomal Histones

Published on: July 25, 2019

Area of Science:

Biochemistry
Structural Biology
Spectroscopy

Background:

Protein structure and function are critically dependent on conformational flexibility.
Understanding protein behavior under extreme conditions like low temperatures is vital for various applications.

Purpose of the Study:

To investigate the structural integrity and dynamics of ubiquitin in supercooled water at low temperatures.
To identify early molecular events associated with cold-denaturation in proteins.

Main Methods:

Nuclear Magnetic Resonance (NMR) spectroscopy was employed to probe ubiquitin structure.
Experiments were conducted in supercooled water solutions at temperatures down to 263 K.

Main Results:

Ubiquitin maintains a folded state down to 263 K, with minor rearrangements in its hydrophobic core.
Non-linear temperature dependence of amide proton chemical shifts and weakening of backbone hydrogen bonds were observed in the cold-denaturation-prone region.
The identified region showing hydrogen bond weakening is also involved in ubiquitin-protein complex formation.

Conclusions:

Weakening of beta-sheet hydrogen bonds may be an initial step in ubiquitin cold-denaturation.
The structural plasticity of this region facilitates conformational adjustments necessary for ubiquitin complex formation.