An α-helix would be destabilized most by:

• A. DNA missense mutation leading to a Gly residue placed in the α-helix sequence.
• B. Interactions between neighboring Asp & Arg residues.
• C. A hydrophobic environment competing for hydrogen bonds.
• D. DNA missense mutation leading to a Pro residue placed in the α-helix sequence.
• E. A net electric dipole spanning several peptide bonds throughout the α-helix.

Answer: (D)

Verified step by step guidance

1. Understand the structure of an α-helix: It is a common secondary structure in proteins characterized by a right-handed coil where each backbone N-H group forms a hydrogen bond with the C=O group of the amino acid four residues earlier.
2. Consider the role of amino acids in α-helix stability: Certain amino acids, like proline, can disrupt the α-helix due to their unique structure. Proline lacks a hydrogen atom on its nitrogen, preventing it from participating in hydrogen bonding, and its rigid ring structure introduces a kink in the helix.
3. Evaluate the impact of a DNA missense mutation: A missense mutation can lead to the substitution of one amino acid for another in the protein sequence. If proline is introduced into an α-helix, it can destabilize the helix due to its structural constraints.
4. Analyze the effects of neighboring Asp and Arg residues: These residues can form salt bridges, which might stabilize the α-helix rather than destabilize it, unless they are positioned in a way that disrupts the helix's regular structure.
5. Consider environmental factors: A hydrophobic environment might compete for hydrogen bonds, but the introduction of proline directly into the helix sequence is more disruptive due to its inability to maintain the regular hydrogen bonding pattern necessary for α-helix stability.