Structural dynamics of the M4 transmembrane segment during acetylcholine receptor gating.
The transition state structures that link the stable end states of allosteric proteins are largely unresolved. We used single-molecule kinetic analysis to probe the dynamics of the M4 transmembrane segments during the closed<==>open isomerization of the neuromuscular acetylcholine receptor ion channel (AChR). We measured the slopes (phi) of the free energy relationships for 87 mutants, which reveal the open- versus closed-like characters of the mutated residues at the transition state and hence the sequence and organization of gating molecular motions. phi was constant throughout the length of the alpha subunit M4 segment with an average value of 0.54, suggesting that this domain moves as a unit, approximately midway through the reaction. Analysis of a hybrid construct indicates that the two alpha subunits move synchronously. Between subunits, the sequence of M4 motions is alpha-epsilon-beta. The AChR ion channel emerges as a dynamic nanomachine with many moving parts.
Center for Single-Molecule Biophysics, Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214, USA.
Ananya
A
Mitra
Timothy D
TD
Bailey
Anthony L
AL
Auerbach
D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D004594:Electrophysiology; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D051379:Mice; D009154:Mutation / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000235:genetics / Q000502:physiology
D021122:Protein Subunits; D011978:Receptors, Nicotinic