What distance between the acetyl O and N of acetylcholine supports activation of nicotinic receptors?

What distance between the acetyl O and N of acetylcholine supports activation of nicotinic receptors?

• A. 3.0 Angstroms
• B. 4.4 Angstroms
• C. 5.9 Angstroms
• D. 6.5 Angstroms

Answer: (C)

Activation of the nicotinic receptor hinges on acetylcholine adopting a geometry in the binding pocket that can engage key interactions at once. The quaternary ammonium nitrogen provides the essential positive charge that fits into the aromatic cage of the pocket, producing strong cation-π interactions, while the acetyl oxygen participates in stabilizing contacts such as hydrogen bonding with nearby residues. The distance between these two functional groups needs to be just right to allow both interactions to occur without strain. About 5.9 Angstroms places the N+ in the optimal position to interact with the aromatic residues and lets the ester oxygen participate in the stabilizing contacts, promoting the conformational changes that open the channel. If the distance is shorter, the groups can't align properly and the interactions weaken; if it’s longer, the molecule stalls in an unfavorable pose and binding energy drops. So this roughly 6 Å separation best supports receptor activation.

Activation of the nicotinic receptor hinges on acetylcholine adopting a geometry in the binding pocket that can engage key interactions at once. The quaternary ammonium nitrogen provides the essential positive charge that fits into the aromatic cage of the pocket, producing strong cation-π interactions, while the acetyl oxygen participates in stabilizing contacts such as hydrogen bonding with nearby residues. The distance between these two functional groups needs to be just right to allow both interactions to occur without strain. About 5.9 Angstroms places the N+ in the optimal position to interact with the aromatic residues and lets the ester oxygen participate in the stabilizing contacts, promoting the conformational changes that open the channel. If the distance is shorter, the groups can't align properly and the interactions weaken; if it’s longer, the molecule stalls in an unfavorable pose and binding energy drops. So this roughly 6 Å separation best supports receptor activation.