Membrane cholesterol regulates inhibition and substrate transport by the glycine transporter, GlyT2
Membrane cholesterol binds to and modulates the function of the specific SLC6 transporters. Here we investigate how cholesterol binds to and modulates the rate of glycine transport by the SLC6 glycine transporter GlyT2, and how this impacts lipid inhibition of GlyT2. Bioactive lipid inhibitors of GlyT2 are analgesics that bind to the lipid allosteric site of the outward facing GlyT2 conformation that is accessible from the extracellular solution. Using molecular dynamics simulations, mutagenesis and cholesterol depletion experiments, we show that bioactive lipid inhibition of glycine transport is modulated by the recruitment of membrane cholesterol to a cholesterol binding site formed by transmembrane helices 1, 5 and 7. Recruitment involves cholesterol flipping from its membrane orientation, and insertion of the 3 hydroxyl group into the cholesterol binding cavity to interact with the base of the lipid allosteric site and the bound inhibitor. The recruitment of membrane cholesterol by allosteric GlyT2 inhibitors is a potential avenue for the development of high-potency, specific pain analgesics and could provide alternative therapeutics that target GlyT2 and other SLC6 neurotransmitter transporters.