Question

Question: Explain why Pro residues can occupy the N-terminal turn of an$\mathrm{\alpha }$helix.

Short answer

Due to Proline Pro residues can occupy the N-terminal turn of an $\mathrm{\alpha }$ helix as they do not clash with other residues.-

Step-by-step solution

Concept Introduction

Every backbone $\mathbf{C}\mathbf{=}\mathbf{O}$group in the right-hand helix shape known as the alpha helix ($\mathbf{\alpha }$-helix) forms a hydrogen bond with the backbone group of the amino acid that is four residues earlier in the protein sequence.

Pro Residues occupying N-terminal turn of Helix

The pyrrolidine ring of Pro in the interior of an$\mathrm{\alpha }$ helix sterically interferes with the residue one turn towards the N-terminus. Pro residues in the N-terminal turn of an helix do not clash with other residues so it can occupy the N-terminal turn of an helix.

Therefore, the major reason is Proline.