Question

Why must multiple ubiquitins be attached to proteins prior to degradation rather than just one or two?

1) Proteosome binding sites are so large that a large surface is required
2) Mis-folded and ubiquitnated proteins link together to form long chains, making their digestion easier
3) To minimize their efforts, making them easier to capture
4) To allow the mis-folded protein to possibly recover, thus rescuing a large energy investment

Answer 1

Proteins must have multiple ubiquitins attached to them prior to degradation because this forms a necessary poly-ubiquitin chain that the proteasome can recognize and bind, allowing the protein to be effectively targeted for breakdown.

Step-by-step explanation:

Multiple ubiquitins must be attached to proteins prior to degradation because proteosome binding sites require a large poly-ubiquitin chain to recognize and bind the protein effectively. This multi-ubiquitin tagging acts like a flag signaling that the protein's lifespan is complete and it is ready for degradation.

The process begins with ubiquitin molecules attaching to the target protein. Subsequent ubiquitins form a chain, resulting in a poly-ubiquitinated protein that delivers itself to the proteasome. The proteasome, facilitated by the 19S 'CAP' structure, recognizes the poly-ubiquitin tags, unfolds the protein using ATP hydrolysis, and allows its entry into the core for degradation. This specificity in degradation helps maintain cellular proteostasis and regulates gene expression by controlling protein longevity.