Where is the greatest likelihood of the occurrence of a proline residue in a protein structure?
Where is the greatest likelihood of the occurrence of a proline residue in a protein structure?
Select an option to attempt
Correct Answer: Option C
Explanation
Proline in protein structure: turns and loops:Proline is a unique amino acid with a pyrrolidine ring side chain that is covalently bonded to its own backbone nitrogen:• This ring structure constrains the backbone torsion angle(fixed).• This rigidity makes proline INCOMPATIBLE with regular secondary structures:--helix: Pro disrupts the regular H-bonding pattern (no NH hydrogen to donate — the nitrogen is in the ring) → called a 'helix breaker'--sheet: Pro's fixedangle does not fit theangles required for-sheets• Pro is most commonly found in:- TURNS (especially Type I and Type II-turns, position i+1)- LOOPS and coil regions where backbone flexibility requirements are less strict- At the beginning of-helices where it can be accommodatedStatistical analysis of protein structures confirms enrichment of Pro at turns and loops.Answer: Proline's fixedangle makes it a helix/sheet breaker; found most commonly in turns and loops.