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The position of an arginine residue influences substrate affinity and K + coupling in the human glutamate transporter, EAAT1
Author(s) -
Ryan Renae M.,
Kortt Nicholas C.,
Sirivanta Tan,
Vandenberg Robert J.
Publication year - 2010
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.2010.06796.x
Subject(s) - transporter , arginine , biophysics , biochemistry , chemistry , glutamate receptor , pyrococcus horikoshii , amino acid , stereochemistry , biology , receptor , enzyme , gene
J. Neurochem. (2010) 114 , 565–575. Abstract Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system and extracellular glutamate levels are controlled by a family of transporters known as excitatory amino acid transporters (EAATs). The EAATs transport glutamate and aspartate with similar micromolar affinities and this transport is coupled to the movement of Na + , K + , and H + . The crystal structure of a prokaryotic homologue of the EAATs, aspartate transporter from Pyrococcus horokoshii (Glt Ph ), has yielded important insights into the architecture of this transporter family. Glt Ph is a Na + ‐dependent transporter that has significantly higher affinity for aspartate over glutamate and is not coupled to H + or K + . The highly conserved carboxy‐terminal domains of the EAATs and Glt Ph contain the substrate and ion binding sites, however, there are a couple of striking differences in this region that we have investigated to better understand the transport mechanism. An arginine residue is in close proximity to the substrate binding site of both Glt Ph and the EAATs, but is located in transmembrane domain (TM) 8 in the EAATs and hairpin loop 1 (HP1) of Glt Ph . Here we report that the position of this arginine residue can explain some of the functional differences observed between the EAATs and Glt Ph . Moving the arginine residue from TM8 to HP1 in EAAT1 results in a transporter that has significantly increased affinity for both glutamate and aspartate and is K + independent. Conversely, moving the arginine residue from HP1 to TM8 in Glt Ph results in a transporter that has reduced affinity for aspartate.