What are Chaperones and Chaperonins?

Chaperones are specialized proteins that help to maintain proper protein folding and to prevent their aggregation during the synthesis and transport of protein molecules.

Chaperones are proteins that interact with partially folded or misfolded proteins to guide them to the correct conformation or might even target them for degradation.

What is Protein Folding?

Protein folding is a process by which a protein molecule acquires its native three-dimensional structure from its linear amino acid sequence. This process is essential for the proper function of a protein, as the final three-dimensional structure determines its biological activity.

Protein folding occurs spontaneously inside the cell but is influenced by various factors such as temperature, pH, and the presence of other proteins and cofactors.

The folding process is aided by chaperones, which assist in maintaining the correct conformation and preventing misfolding and aggregation. Misfolded proteins can lead to cellular damage and various diseases, such as Alzheimer’s and Huntington’s disease.

Why is protein folding important?

Proteins are highly complex biomolecules that perform a wide array of functions in cells. They catalyze reactions (enzymes), transport molecules (transport proteins), and transmit signals (neurotransmitters).

These functions are made possible by a unique three-dimensional structure of a protein.

In order to perform its function correctly, the protein must fold into its correct conformational three-dimensional structure. Proteins in this structure are thermodynamically stable with the minimum energy state and without any conformational and steric hindrances between amino acid residues – due to hydrogen bonds, hydrophobic interactions, and ionic bonds.

If a protein does not fold correctly, it becomes non-functional. Also, misfolded proteins might form harmful structures; for eg. amyloid fibrils which contribute to the development of diseases such as Alzheimer’s, Huntington’s, and other neurodegenerative disorders.

Hence, protein folding is critical for proper functioning.

When does protein folding take place?

Protein folding occurs after a protein is synthesized on ribosomes and released into the cytoplasm.

Originally in the linear chain of amino acids, the polypeptide chain then spontaneously folds into its unique three-dimensional structure. This process can take anywhere from milliseconds to minutes, depending on the size and complexity of the protein.

The folding process is influenced by various factors as already mentioned (temperature, pH, etc).

Proper protein folding is crucial for the function of a protein because the final three-dimensional structure determines the optimal biological activity of the protein.

Misfolded proteins can lead to cellular damage and various diseases.

The Structure of Chaperones

The basic structure of chaperones can vary depending on their types. However, most of them share certain structural features that allow them to perform their roles in protein folding and preventing aggregation.

Some of their structural features are:

Hydrophobic surface – Most chaperones have hydrophobic surfaces that allow them to interact with partially folded or misfolded proteins.
ATP-binding domains – Chaperones bind to ATP (adenosine triphosphate), which provides energy for the chaperoning process.
The peptide-binding domains – Chaperones have peptide-binding domains to allow them to interact with newly synthesized proteins.
Specific recognition sequences – Most chaperones often have specific recognition sequences needed to distinguish between properly folded and misfolded proteins.
Multiple subunits – Chaperonins are a specific type of chaperone. They are composed of multiple subunits to form a protein complex, capable of assisting in protein folding.

What are the types of chaperones?

Chaperones are a diverse group of proteins that play a role in maintaining proper protein folding and stability. Some common types of known chaperones are:

Hsp70 – The heat shock protein 70 helps prevent protein aggregation and the refolding of denatured proteins.
Hsp60 – The heat shock protein 60 folds newly synthesized proteins and assists in the assembly of protein complexes.
Hsp90 – It works to stabilize certain signaling proteins.
Small heat shock proteins – The small heat shock proteins act as molecular chaperones. They also prevent protein aggregation and assist in the refolding of denatured proteins.
chaperonins – Chaperonins are somewhat large cylindrical protein complexes that help to fold the newly synthesized proteins.
Clp (caseinolytic protease) – Clp is a protease that degrades misfolded proteins. The process also utilizes the co-chaperones.

What are Chaperonins?

Chaperonins are large cylindrical protein complexes that assist in the folding of newly synthesized proteins.

Chaperonins’ structure is composed of two stacked rings, each with a central cavity where the process of protein folding occurs.

This cavity is a protected environment that prevents nascent polypeptides from coming into contact with other cellular components. If these nascent polypeptides come in contact with other components, might result in reactions or misfolding.

The chaperonin cycle operates to recognize partially folded or unfolded protein. Then it is encapsulated within the central cavity and with the guidance of the chaperonin the protein is folded to its native or biologically active conformation.

Chaperonins play a critical role in maintaining proper protein folding. Hence, they are highly essential for cellular protein homeostasis.

Chaperonins have been implicated in various diseases that consist including neurodegenerative disorders, cancer, etc. They have been the central subject of research for their potential to act as therapeutic targets.