What is the Difference Between Lysosome and Proteasome

The main difference between lysosome and proteasome is that lysosome degrades extracellular and cell-surface membrane proteins, whereas proteasome degrades intracellular proteins.

Lysosome and proteasome are two intracellular devices that break down damaged and unneeded proteins. Protein degradation is important to supply amino acids for fresh protein synthesis, to remove excess enzymes, and to remove unneeded transcription factors. 

Key Areas Covered

1. What is Lysosome
– Definition, Facts, Importance
2. What is Proteasome
– Definition, Facts, Importance
3. Similarities Between Lysosome and Proteasome
– Outline of Common Features
4. Difference Between Lysosome and Proteasome
– Comparison of Key Differences

Key Terms  

Lysosome, Proteasome

What is Lysosome

Lysosome is a proteolytic machinery responsible for the protein degradation through autophagy. Autophagy is an important process for determining protein quality and quality control. It recycles damaged proteins, aggregates, and organelles in the cell, clearing up the cell and providing building blocks to replace the depleted cellular components. Also, it protects against the stress created by nutrient deprivation as well. Autophagy is pro-survival, allowing the cell to undergo stress.

Figure 1: Lysosome

Furthermore, the lysosome is a membrane-enclosed vacuole in the cytoplasm containing hydrolytic enzymes. A lysosome’s main function is to help digest biomolecules like lipids, nucleic acids, peptides, carbohydrates, etc. The hydrolytic enzymes in the lysosome occur in the endoplasmic reticulum. They travel from the cis phase of the Golgi apparatus to the trans phase by packaging in secretory vesicles. Finally, they leave the trans phase of the Golgi apparatus as lysosomes. Also, the pH of the cytoplasm is around 7.2. However, the pH inside a lysosome is 4.5-5.0. That means the internal environment of the lysosome is acidic. It is due to the requirement of an acidic pH by the action of the hydrolytic enzymes in the lysosome.

What is Proteasome

The proteasome is another proteolytic machinery responsible for protein degradation through the ubiquitin-proteasome system (UPS). It is also important for protein quality control. Additionally, it undergoes proteolysis, the breakdown of peptide bonds. Importantly, ubiquitin is the small protein that tags the proteins that need to be degraded. Ubiquitin ligases are the enzymes that catalyze the tagging reaction. Also, an addition of a single ubiquitin molecule to the degradable protein induces the addition of more ubiquitin molecules to the protein. Then, it forms a polyubiquitin chain that binds to the proteasome to degrade the tagged protein.

Figure 2: Proteasome

Moreover, the degradation produces peptides that are seven to eight amino acids long. Further, they are degraded into shorter amino acid sequences that can be used in synthesizing new proteins. Proteasomes occur in eukaryotes, archaea, and bacteria. 

Similarities Between Lysosome and Proteasome

• Lysosome and proteasome are two protein degradation machinery inside the cell.
• They are important to supply amino acids for fresh protein synthesis, to remove excess enzymes, and to remove unneeded transcription factors.

Difference Between Lysosome and Proteasome

Definition

Lysosome refers to a membrane-bound cell organelle that contains digestive enzymes. In contrast, proteasome refers to a complex of proteinases involved in breaking down selected intracellular proteins.  

Type of Proteins

Lysosome degrades extracellular and cell-surface membrane proteins, while proteasome degrades intracellular proteins.

Process

Lysosome degrades cytoplasmic components, defective or surplus organelles, protein aggregates, and individual proteins through autophagy, while proteasome degrades individual cellular proteins in a targeted manner with the use of the ubiquitin-proteasome system (UPS). 

Conclusion

In brief, lysosome and proteasome are two protein degradation machinery inside the cell. Lysosome degrades extracellular and cell-surface membrane proteins through autophagy. The types of proteins degraded by lysosomes include cytoplasmic components, defective or surplus organelles, protein aggregates, and individual proteins. In comparison, proteasome degrades intracellular proteins. Importantly, it uses a ubiquitin-proteasome system (UPS) for the degradation of proteins in a targeted manner. Therefore, the main difference between lysosome and proteasome is the type of proteins degraded by each machinery. 

References:

1. Wang X, Robbins J. Proteasomal and lysosomal protein degradation and heart disease. J Mol Cell Cardiol. 2014 Jun;71:16-24. doi: 10.1016/j.yjmcc.2013.11.006. Epub 2013 Nov 14. PMID: 24239609; PMCID: PMC4011941.

Image Courtesy:

1. “Figure 42 02 01” By CNX OpenStax – Own Work (CC-BY 4.0) via Commons Wikimedia
2. “Proteaosome 1fnt side” By Thomas Splettstoesser – Own work (CC-BY SA 3.0) via Commons Wikimedia