What is the Difference Between P-bodies and Stress Granules

P-bodies and stress granules are two structures in the cytosol of the eukaryotic cell. Both are composed of RNA and proteins. Both are biomolecular condensates formed in the cell. The formation of P-bodies and stress granules can be caused by both exogenous and endogenous factors, such as temperature, oxidative and osmotic stress, etc. Furthermore, the most studied membrane-less organelles (MLOs) formed in response to stress in eukaryotic cells are P-bodies and stress granules.

The key difference between P-bodies and stress granules is their composition. P-bodies are cytoplasmic ribonucleoprotein granules composed of translationally repressed mRNAs and proteins associated with mRNA decay, while stress granules are cytoplasmic membrane-less compartments composed of proteins and mRNAs such as poly(A)+ mRNA.

CONTENTS

1. Overview and Key Difference
2. What are P-bodies  
3. What are Stress Granules
4. Similarities – P-bodies and Stress Granules
5. P-bodies vs Stress Granules in Tabular Form
6. Summary – P-bodies vs Stress Granules
7. FAQ – P-bodies and Stress Granules

What are P-bodies?

P-bodies are also known as processing bodies. They are evolutionarily conserved in eukaryotes, and they also possess the characteristics of liquid droplets. P-bodies are primarily composed of translationally repressed mRNAs and proteins associated with mRNA decay machinery. Moreover, P-bodies contain mRNA decay intermediates.

Figure 01: P-bodies

Proteins in P-bodies include cytoplasmic deadenylase complex, decapping coactivator and enzyme, decapping activators, 5’-3’ exoribonuclease, and RNA-binding proteins. Furthermore, P-bodies may act as reservoirs to store translationally repressed mRNAs and inactive decapping enzymes.

What are Stress Granules?

Stress granules are biomolecular condensates in the cytosol of eukaryotes. They are composed of proteins and RNA that assemble into 0.1–2 μm membrane-less organelles when the cell is under stress. Stress granules are also stalled translation pre-initiation complexes and have mRNA associated with 40S ribosomal subunits, translation initiation factors, and RNA-binding proteins (RBPs).

Figure 02: Stress Granules

Stress granules are said to be associated with the endoplasmatic reticulum. Furthermore, stress granules can protect RNA from harmful conditions and chemicals.

Similarities Between P-bodies and Stress Granules

1. P-bodies and stress granules are two biomolecular condensates in the cytosol of the eukaryotic cell.
2. Both are composed of RNA and proteins.
3. They are the most studied membrane-less organelles formed in response to stress in eukaryotic cells.
4. They are directly involved in the regulation of a large number of signalling pathways.
5. The transformation of P-bodies and stress granules into MLOs containing amyloid fibrils results in neurodegenerative diseases.

Difference Between P-bodies and Stress Granules

Definition

1. P-bodies are cytoplasmic ribonucleoprotein (RNP) granules composed of translationally repressed mRNAs and proteins related to mRNA decay machinery.
2. Stress granules are cytoplasmic stalled translation pre-initiation complexes that have poly(A)+ mRNAs associated with proteins.

Size

1. P-bodies are 100–300 nm in diameter.
2. Stress granules are 0.1 to 2.0 μm in diameter.

Types of Proteins in the Structure

1. Proteins in P-bodies include cytoplasmic deadenylase complex, decapping coactivator and enzyme, decapping activators, 5’-3’ exoribonuclease, and RNA-binding proteins.
2. Proteins in stress granules include 40S ribosomal subunits, translation initiation factors, and RNA-binding proteins (RBPs).

Function

1. P-bodies may act as reservoirs to store translationally repressed mRNAs and inactive decapping enzymes.
2. Stress granules are associated with the endoplasmatic reticulum and protect RNA from harmful conditions and chemicals.

Associated Diseases

1. P-bodies are associated with Parkinson’s disease.
2. Stress granules are associated with cancer, viral infections, and Alzheimer’s disease.

The following table summarizes the difference between P-bodies and stress granules.

Summary – P-bodies vs Stress Granules

P-bodies and stress granules are cytoplasmic membrane-less organelles formed in response to stress in eukaryotic cells. They are associated with a large number of signalling pathways. P-bodies are cytoplasmic ribonucleoprotein (RNP) granules that contain mRNAs, RNA-binding proteins, and effectors of mRNA turnover, while stress granules are non-enveloped structures formed via poly(A)+ mRNA and protein aggregation under various stress conditions. This summarizes the difference between P-bodies and stress granules.

FAQ: P-bodies and Stress Granules

1. What is the condensation of biomolecules?

• Condensation is a chemical process by which two molecules are joined together to make a larger, more complex molecule with the loss of water. Carbohydrates, proteins, lipids, and nucleic acids are macromolecules formed by the condensation of biomolecules.

2. Where are P-bodies found in the cell?

• P-bodies are dynamic ribonucleoprotein granules found in the cytoplasm of the cell. They are primarily composed of translationally repressed mRNAs and proteins associated with mRNA decay.

3. What is the role of the P-bodies?

• P-bodies function as sites of both RNA degradation and RNA storage. They are thought to have an important role in regulating translation. They also act as reservoirs to store inactive decapping enzymes.

4. Do stress granules contain ribosomes?

• Stress granules are primarily composed of stalled 48S complexes containing poly(A)+ mRNA bound to early initiation factors such as eIF4E, eIF3, eIF4A, eIFG, and small ribosomal subunits.

5. Why are stress granules important?

• Stress granules are distinct RNA granules produced when cells are under various stresses, which are evolutionarily conserved across species. In general, stress granules act as a conservative and essential self-protection mechanism for RNA molecules during stress responses.

Reference:

1.   “P-Bodies: Composition, Properties, and Functions.” ACS Publications.
2.  “Stress Granule – An Overview.” ScienceDirect.

Image Courtesy:

1. “P bodies in a Drosophila embryo” By The Journal of Cell Biology (CC BY-NC-SA 2.0) via Flickr

2. “ALS Disease Pathology and Proposed Disease Mechanisms” By Philip Van Damme, Wim Robberecht, and Ludo Van Den Bosch – “Modelling amyotrophic lateral sclerosis: progress and possibilities.” Disease Models and Mechanisms. 10 (5): 537-549. doi:10.1242/dmm.029058 PMC: 5451175 PMID: 28468939. (CC BY 3.0) via Commons Wikimedia

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