PDBsum entry 3f3d

Transport protein

PDB id

3f3d

Contents

			Protein chain

					509 a.a.

			Ligands

					BOG ×5


					MET

			Metals

					_NA ×2

			Waters ×53

References listed in PDB file

Key reference

Title

A competitive inhibitor traps leut in an open-To-Out conformation.

Authors

S.K.Singh, C.L.Piscitelli, A.Yamashita, E.Gouaux.

Ref.

Science, 2008, 322, 1655-1661. [DOI no: 10.1126/science.1166777]

PubMed id

19074341

Note: In the PDB file this reference is annotated as "TO BE PUBLISHED". The citation details given above have been manually determined.

Abstract

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.



	Figure 4. Fig. 4. A second Trp molecule is bound between R30 and D404 of the extracellular gate only in the open-to-out conformation. (A) Trp602 bound in the extracellular vestibule of LeuT, residing between D404 and R30, flanked by the -helix in TM10. (B) Extracellular vestibule of the LeuT-SeMet complex. Anomalous-difference Fourier map (contoured at 5 and 15 and depicted in green and blue mesh, respectively) showing no substantial density peaks in the extracellular vestibule.		Figure 5. Fig. 5. Schematic of transport and inhibition in LeuT. Postulated conformational changes associated with isomerization from the open-to-out (A) to the outward-facing occluded state (B) on binding of substrate and ions, from the occluded (B) to open-to-in state (C) and dissociation of transported substrate and ions, and from the open-to-in (C) back to the open-to-out state (A). (D) Effect of the competitive inhibitor Trp on transport: stabilizing the open-to-out conformation. (E) Effect of the noncompetitive TCA inhibitors on transport-stabilizing the outward-facing occluded conformation. The boxed conformations represent actual crystal structures, whereas the unboxed conformations are hypothetical.

PROCHECK

	Headers