Which system was recognized with the 2004 Nobel Prize for the discovery of ubiquitin-mediated protein degradation?

Which system was recognized with the 2004 Nobel Prize for the discovery of ubiquitin-mediated protein degradation?

• A. Lysosome
• B. Autophagy
• C. Ubiquitin/Proteasome system
• D. Endocytosis

Answer: (C)

Proteins targeted for removal are tagged with ubiquitin, and this ubiquitin tag directs them to the proteasome for breakdown in an ATP-dependent process. This ubiquitin–proteasome system, consisting of the tagging enzymes E1, E2, and E3 and the 26S proteasome that degrades the tagged proteins, was recognized with the 2004 Nobel Prize for its discovery. This pathway tightly controls protein levels and functions, regulates the cell cycle, and maintains protein quality, making it fundamental to many cellular processes. The other options involve different routes of degradation—lysosome-driven autophagy and endocytosis are separate pathways—so they do not represent the system honored by the Nobel Prize.

Proteins targeted for removal are tagged with ubiquitin, and this ubiquitin tag directs them to the proteasome for breakdown in an ATP-dependent process. This ubiquitin–proteasome system, consisting of the tagging enzymes E1, E2, and E3 and the 26S proteasome that degrades the tagged proteins, was recognized with the 2004 Nobel Prize for its discovery. This pathway tightly controls protein levels and functions, regulates the cell cycle, and maintains protein quality, making it fundamental to many cellular processes. The other options involve different routes of degradation—lysosome-driven autophagy and endocytosis are separate pathways—so they do not represent the system honored by the Nobel Prize.