Ichia Chen, Shashank Pant, Qianyi Wu, Rosemary Cater, Meghna Sobti, Robert
Vandenberg, Alastair G. Stewart, Emad Tajkhorshid, Josep Font, and Renae
Ryan.
Glutamate transporters have a chloride channel with two hydrophobic
gates.
Nature, 591:327-331, 2021.
CHEN2021-ET
Glutamate is the most abundant excitatory neurotransmitter in the
central nervous system, therefore its precise control is vital for
maintaining normal brain function and preventing excitotoxicity.
Removal of extracellular glutamate is achieved by plasma membrane-
bound transporters, which couple glutamate transport to sodium,
potassium and pH gradients using an elevator mechanism. Glutamate
transporters also conduct chloride ions via a channel-like process
that is thermodynamically uncoupled from transport. However, the
molecular mechanisms that allow these dual-function transporters
to carry out two seemingly contradictory roles are unknown. Here we
report the cryo-electron microscopy structure of a glutamate
transporter homologue in an open-channel state, revealing an aqueous
cavity that is formed during the transport cycle. By studying
functional properties combined with molecular dynamics simulations,
we show that this cavity is an aqueous-accessible chloride
permeation pathway gated by two hydrophobic regions and is
conserved across mammalian and archaeal glutamate transporters. Our
findings provide insight into the mechanism by which glutamate
transporters support their dual function and add a crucial piece of
information to aid mapping of the complete transport cycle shared by
the SLC1A transporter family.
