Internal dynamics of the nicotinic acetylcholine receptor in reconstitutedmembranes

The structure and H-1/H-2 exchange kinetics of affinity-purified nAChR reco nstituted into egg phosphatidylcholine membranes with increasing levels of either dioleoylphosphatidic acid (DOPA) or cholesterol (Chol) have been exa mined using infrared spectroscopy. All spectra of the reconstituted nAChR m embranes recorded after 72 h in (H2O)-H-2 exhibit comparable amide I band s hapes, suggesting a similar secondary structure for the nAChR in each lipid environment. Increasing levels of either DOPA or Chol, however, lead to an increasing intensify of the amide II band, indicating a decreasing proport ion of nAChR peptide hydrogens that have exchanged for deuterium. Spectra r ecorded as a function of time after exposure of the nAChR to (H2O)-H-2 show that the presence of either lipid slows down the H-1/H-2 exchange of those peptide hydrogens that normally exchange on the minutes to hours time scal e. The slowing of peptide H-1/H-2 exchange correlates with both an increasi ng ability of the nAChR to undergo agonist-induced conformational change [B aenziger, J. E., Morris, M.-L., Darsaut, T. E., and Ryan, S. E. (1999) in p reparation] and possibly a decreasing membrane fluidity. Our data suggest t hat lipid composition dependent changes in nAChR peptide H-1/H-2 exchange k inetics reflect altered internal dynamics of the nAChR. Lipids may influenc e protein function by changing the internal dynamics of integral membrane p roteins.