Singh Satinder K, Piscitelli Chayne L, Yamashita Atsuko, Gouaux Eric
Vollum Institute, Oregon Health and Science University, 3181 Southwest Sam Jackson Park Road, Portland, OR 97239, USA.
Science. 2008 Dec 12;322(5908):1655-61. 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.
次级转运蛋白是细胞膜的主力军，催化小分子和离子跨双层膜的移动，并将底物通过与离子梯度相偶联。然而，伴随底物转运的构象变化、底物通过转运蛋白的机制以及竞争性抑制的原理仍不清楚。我们对亮氨酸转运蛋白（LeuT）进行了晶体学和功能研究，LeuT是神经递质钠同向转运体的一个模型，结果表明各种氨基酸底物诱导相同的闭锁构象状态，并且一种竞争性抑制剂色氨酸（Trp）将LeuT捕获在一种由外向内开放的构象中。在Trp复合物中，细胞外门控残基精氨酸30和天冬氨酸404在底物或抑制剂从细胞外溶液渗透到主要底物位点时，为它们定义了第二个弱结合位点，这表明参与门控的残基也介导渗透作用。
