What is a chaperone protein and what is its role in protein folding?

• A. Chaperones assist nascent polypeptides to fold correctly and prevent aggregation.
• B. Chaperones degrade misfolded proteins.
• C. Chaperones act as ribosome subunits.
• D. Chaperones are enzymes that phosphorylate proteins.

Answer: (A)

Chaperone proteins help newly made polypeptides fold into their correct shapes and prevent them from sticking together into problematic aggregates. As a protein is being synthesized, parts of it are exposed that could cause misfolding or clumping if left unassisted. Chaperones bind to these exposed regions, stabilize the chain, and often create a protected environment or use ATP-driven cycles to guide proper folding. This support can occur while the protein is still being translated on the ribosome or after it has been released.

Many chaperones act in different ways. Some (like Hsp70 family members) bind temporarily to nascent chains to prevent premature folding or aggregation, while others (chaperonins such as GroEL/GroES) provide an isolated chamber where a polypeptide can fold without interference from other cellular proteins. This function is distinct from degradation or enzymatic modification: chaperones don’t primarily break down proteins or add phosphate groups; degradation is typically handled by proteases or the ubiquitin–proteasome system, and phosphorylation is done by kinases.

So, the best description is that chaperones assist polypeptides to fold correctly and prevent aggregation.