title: Molecular dynamics simulations of the mammalian glutamate transporter EAAT3.
abstract: Excitatory amino acid transporters (EAATs) are membrane proteins that enable sodium-coupled uptake of glutamate and other amino acids into neurons. Crystal structures of the archaeal homolog GltPh have been recently determined both in the inward- and outward-facing conformations. Here we construct homology models for the mammalian glutamate transporter EAAT3 in both conformations and perform molecular dynamics simulations to investigate its similarities and differences from GltPh. In particular, we study the coordination of the different ligands, the gating mechanism and the location of the proton and potassium binding sites in EAAT3. We show that the protonation of the E374 residue is essential for binding of glutamate to EAAT3, otherwise glutamate becomes unstable in the binding site. The gating mechanism in the inward-facing state of EAAT3 is found to be different from that of GltPh, which is traced to the relocation of an arginine residue from the HP1 segment in GltPh to the TM8 segment in EAAT3. Finally, we perform free energy calculations to locate the potassium binding site in EAAT3, and find a high-affinity site that overlaps with the Na1 and Na3 sites in GltPh.
authors.affiliation: School of Physics, University of Sydney, NSW, Australia.
authors.forename: Germano
authors.initials: G
authors.lastname: Heinzelmann
authors.affiliation: School of Physics, University of Sydney, NSW, Australia.
authors.forename: Serdar
authors.initials: S
authors.lastname: Kuyucak
mesh_terms: D000818:Animals; D001665:Binding Sites; D050580:Excitatory Amino Acid Transporter 3 / Q000737:chemistry*; D018698:Glutamic Acid / Q000737:chemistry*; D006801:Humans; D015640:Ion Channel Gating; D056004:Molecular Dynamics Simulation; D011188:Potassium / Q000737:chemistry*; D011485:Protein Binding; D055503:Protein Multimerization; D051381:Rats; D012964:Sodium / Q000737:chemistry*; D040681:Structural Homology, Protein; D013816:Thermodynamics
chemical_list: D050580:Excitatory Amino Acid Transporter 3; C493400:SLC1A1 protein, human; C493398:Slc1a1 protein, rat; D018698:Glutamic Acid; D012964:Sodium; D011188:Potassium