A stepwise mechanism for acetylcholine receptor channel gating.
Muscle contraction is triggered by the opening of acetylcholine receptors at the vertebrate nerve-muscle synapse. The M2 helix of this allosteric membrane protein lines the channel, and contains a 'gate' that regulates the flow of ions through the pore. We used single-molecule kinetic analysis to probe the transition state of the gating conformational change and estimate the relative timing of M2 motions in the alpha-subunit of the murine acetylcholine receptor. This analysis produces a 'Phi-value' for a given residue that reflects its open-like versus closed-like character at the transition state. Here we show that most of the residues throughout the length of M2 have a Phi-value of approximately 0.64 but that some near the middle have lower Phi-values of 0.52 or 0.31, suggesting that alphaM2 moves in three discrete steps. The core of the channel serves both as a gate that regulates ion flow and as a hub that directs the propagation of the gating isomerization through the membrane domain of the acetylcholine receptor.
Purohit
Prasad
P
Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York 14214, USA.
Mitra
Ananya
A
Auerbach
Anthony
A
D000818:Animals; D002460:Cell Line; D015640:Ion Channel Gating; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship
D021122:Protein Subunits; D011950:Receptors, Cholinergic