proteaszóma

The proteaszóma, or proteasome, is a large protein complex found in nearly all eukaryotic cells and some bacteria. It plays a crucial role in the degradation of intracellular proteins, ensuring cellular homeostasis by removing damaged, misfolded, or unnecessary proteins. The proteasome functions as an essential component of the ubiquitin-proteasome system (UPS), a major pathway for selective protein degradation.

The proteasome consists of a barrel-shaped core, known as the 20S proteasome, composed of four stacked rings of protein subunits. Each ring contains seven subunits, arranged symmetrically around a central cavity. The two outer rings are made of seven α-subunits, while the two inner rings consist of seven β-subunits. These β-subunits contain catalytic sites that cleave peptide bonds in target proteins.

Proteins destined for degradation are first tagged with ubiquitin, a small regulatory protein, in a process mediated by three types of enzymes: E1 ubiquitin-activating enzymes, E2 ubiquitin-conjugating enzymes, and E3 ubiquitin ligases. The polyubiquitinated protein is then recognized and threaded into the proteasome’s central cavity through a regulatory particle, known as the 19S cap, which attaches to the ends of the 20S core. The 19S cap unfolds the substrate protein and translocates it into the proteasome, where it is sequentially cleaved into small peptides.

The proteasome is involved in various cellular processes, including antigen presentation, cell cycle regulation, and signal transduction. Dysregulation of proteasomal activity has been linked to diseases such as cancer, neurodegenerative disorders, and immune system dysfunction. Consequently, proteasome inhibitors, such as bortezomib, are used therapeutically to treat certain types of cancer, particularly multiple myeloma. The proteasome’s importance in maintaining cellular health underscores its significance as a key player in molecular biology and medicine.