The individual molecule and its tribe, the nanocluster: the case of the nicotinic acetylcholine receptor
Francisco J. Barrantes, Alejo Mosqueira, Héctor Buena-Maizón and Lucas A.
Saavedra. Laboratory of Molecular Neurobiology, Institute of Biomedical Research, UCA-CONICET. Buenos Aires, Argentina
Understanding synaptic function requires a detailed knowledge of the intervening molecular constituents. In the particular case of the peripheral cholinergic synapse (the neuromuscular junction), the nicotinic acetylcholine receptor (nAChR) plays a central role. We employ a combination of STED nanoscopy with single-molecule STORM superresolution localization microscopy to study the cell-surface topography and translational motion of this neurotransmitter receptor. At the single-track level, the free walks of an individual trajectory are transiently interrupted by confinement sojourns in small nanodomains (~50 nm radius), with millisecond-long lifetimes. The assembly of nAChR nanoclusters occurs in bursts lasting for seconds, separated by periods of cluster disassembly. The two dynamic processes occur in similar spatial scales, but in different time frames and with different cholesterol sensitivities. The ms-long confinement sojourns and the s-long reversible nanoclustering affect all trajectories and determine the resulting macroscopic motional regime and the breadth of the heterogeneity in the ensemble population. The emerging picture is that the nAChR operates in a heterogeneous mixture of translational regimes: anomalous subdiffusive, Brownian and superdiffusive motions, and that these are subject to cholesterol modulation at the cell membrane.