If the side chain of Phe206(5.47) moves away from Asn109(3.37), it will open up Ser112(3.40) for ligand binding. This may disrupt Ser3.40's hydrogen bond with Tyr6.48, along with the steric hindrance from Phe5.47 forcing Tyr6.48 to move downward, pushing on Val247(6.44) and forcing TMR6 to bend, activating the receptor.
OR1A1 is sensitive to aldehydes and alcohols of a certain minimum length; it responds to heptanol and heptanal, but not hexanol or hexanal, for instance. Ligands that are small enough to fit above Phe5.47 probably form a hydrogen bond to Asn3.37, while slightly longer carbon chains would require the extra space to reach Ser3.40.
The very similar OR1A2 is more preferentially tuned to aldehydes than OR1A1 is, and OR1A2 has Lys3.37. Lysine forms Schiff bases with aldehydes, and the residue is capable of reaching Ser3.40 if Phe5.47 is moved out of the way. A serine can stabilize a Schiff base; it's how mice are able to see ultraviolet.
Other receptors that have both a 6.48-3.40 hbond and a 6.55-45.51 hbond like OR1A1 and OR1A2 do, may utilize similar activation methods involving the forcing of Y6.48 into a more cytoplasm-ward orientation.
If the side chain of Phe206(5.47) moves away from Asn109(3.37), it will open up Ser112(3.40) for ligand binding. This may disrupt Ser3.40's hydrogen bond with Tyr6.48, along with the steric hindrance from Phe5.47 forcing Tyr6.48 to move downward, pushing on Val247(6.44) and forcing TMR6 to bend, activating the receptor.
OR1A1 is sensitive to aldehydes and alcohols of a certain minimum length; it responds to heptanol and heptanal, but not hexanol or hexanal, for instance. Ligands that are small enough to fit above Phe5.47 probably form a hydrogen bond to Asn3.37, while slightly longer carbon chains would require the extra space to reach Ser3.40.
The very similar OR1A2 is more preferentially tuned to aldehydes than OR1A1 is, and OR1A2 has Lys3.37. Lysine forms Schiff bases with aldehydes, and the residue is capable of reaching Ser3.40 if Phe5.47 is moved out of the way. A serine can stabilize a Schiff base; it's how mice are able to see ultraviolet.
Other receptors that have both a 6.48-3.40 hbond and a 6.55-45.51 hbond like OR1A1 and OR1A2 do, may utilize similar activation methods involving the forcing of Y6.48 into a more cytoplasm-ward orientation.