Competitive Inhibitor Traps LeuT in an Open-to-Out Conformation

• Published in: Science (American Association for the Advancement of Science) Vol. 322; no. 5908; pp. 1655 - 1661
• Main Authors: Singh, Satinder K, Piscitelli, Chayne L, Yamashita, Atsuko, Gouaux, Eric
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 12.12.2008; The American Association for the Advancement of Science
• Subjects: Amino Acid Transport Systems - antagonists & inhibitors; Amino Acid Transport Systems - chemistry; Amino Acid Transport Systems - metabolism; Amino acids; Amino Acids - metabolism; Amino Acids - pharmacology; Atoms; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Binding Sites; Binding, Competitive; Biological and medical sciences; Biological Transport; Carboxylates; Cellular biology; Crystal structure; Crystallization; Crystallography, X-Ray; Fundamental and applied biological sciences. Psychology; Hydrogen Bonding; Hydrogen bonds; Hydrophobic and Hydrophilic Interactions; Indoles; Ions; Kinetics; Leucine - metabolism; Ligands; Membranes; Models, Biological; Models, Molecular; Molecular biology; Molecular biophysics; Molecules; Protein Conformation; Protein Structure, Tertiary; Research universities; Sodium - metabolism; Structure in molecular biology; Symporters - antagonists & inhibitors; Symporters - chemistry; Symporters - metabolism; Tryptophan - metabolism; Tryptophan - pharmacology; Membrane transport; Aminoacid; Sodium ion; Neurotransmitter; Inhibitor; Leucine; Competitive inhibition; Structure function relationship; Conformation; Crystalline structure
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1166777

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.