A competitive inhibitor traps LeuT in an open-to-out conformation.
Secondary transporters are workhorses of cellular membranes, catalyzing the movement of small molecules and ions across the bilayer and coupling substrate passage to ion gradients. However, the conformational changes that accompany substrate transport, the mechanism by which a substrate moves through the transporter, and principles of competitive inhibition remain unclear. We used crystallographic and functional studies on the leucine transporter (LeuT), a model for neurotransmitter sodium symporters, to show that various amino acid substrates induce the same occluded conformational state and that a competitive inhibitor, tryptophan (Trp), traps LeuT in an open-to-out conformation. In the Trp complex, the extracellular gate residues arginine 30 and aspartic acid 404 define a second weak binding site for substrates or inhibitors as they permeate from the extracellular solution to the primary substrate site, which demonstrates how residues that participate in gating also mediate permeation.
Singh
Satinder K
SK
Vollum Institute, Oregon Health and Science University, 3181 Southwest Sam Jackson Park Road, Portland, OR 97239, USA.
Piscitelli
Chayne L
CL
Yamashita
Atsuko
A
Gouaux
Eric
E
D026905:Amino Acid Transport Systems / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D001692:Biological Transport; D003460:Crystallization; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D008024:Ligands; D008954:Models, Biological; D008958:Models, Molecular; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000378:metabolism; D027981:Symporters / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism / Q000494:pharmacology*
D026905:Amino Acid Transport Systems; D000596:Amino Acids; D001426:Bacterial Proteins; D008024:Ligands; D027981:Symporters; D014364:Tryptophan; D012964:Sodium; D007930:Leucine