Flux coupling in a neuronal glutamate transporter. Crystallographic and computational investigations corroborated these findings by revealing that the ‘humanizing’ mutations favour structurally ‘unlocked’ intermediate states in the transport cycle exhibiting increased solvent occupancy at the interface between the transport domain and the trimeric scaffold. We show that Glt Ph bearing two mutations introduced to impart characteristics of the human transporter exhibits markedly increased transport domain dynamics, which parallels an increased rate of substrate transport, thereby establishing a direct temporal relationship between transport domain motion and substrate uptake. Here we report direct observations of these ‘elevator-like’ transport domain motions in the context of reconstituted proteoliposomes and physiological ion gradients using single-molecule fluorescence resonance energy transfer (smFRET) imaging.
Crystallographic studies of a glutamate transporter homologue from the archaeon Pyrococcus horikoshii, Glt Ph, showed that distinct transport domains translocate substrates into the cytoplasm by moving across the membrane within a central trimerization scaffold. Glutamate transporters terminate neurotransmission by clearing synaptically released glutamate from the extracellular space, allowing repeated rounds of signalling and preventing glutamate-mediated excitotoxicity.
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