Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
Structure. 2022 Jul 7;30(7):1035-1041.e3. doi: 10.1016/j.str.2022.04.011. Epub 2022 May 16.
Mammalian peptide transporters, PepT1 and PepT2, mediate uptake of small peptides and are essential for their absorption. PepT also mediates absorption of many drugs and prodrugs to enhance their bioavailability. PepT has twelve transmembrane (TM) helices that fold into an N-terminal domain (NTD, TM1-6) and a C-terminal domain (CTD, TM7-12) and has a large extracellular domain (ECD) between TM9-10. It is well recognized that peptide transport requires movements of the NTD and CTD, but the role of the ECD in PepT1 remains unclear. Here we report the structure of horse PepT1 encircled in lipid nanodiscs and captured in the inward-open apo conformation. The structure shows that the ECD bridges the NTD and CTD by interacting with TM1. Deletion of ECD or mutations to the ECD-TM1 interface impairs the transport activity. These results demonstrate an important role of ECD in PepT1 and enhance our understanding of the transport mechanism in PepT1.
哺乳动物肽转运蛋白 PepT1 和 PepT2 介导小肽的摄取，是其吸收所必需的。PepT 还介导许多药物和前药的吸收，以提高其生物利用度。PepT 有十二个跨膜 (TM) 螺旋，折叠成一个 N 端结构域 (NTD，TM1-6) 和一个 C 端结构域 (CTD，TM7-12)，并在 TM9-10 之间有一个大的细胞外结构域 (ECD)。人们已经认识到，肽的转运需要 NTD 和 CTD 的运动，但 ECD 在 PepT1 中的作用仍不清楚。本文报道了包埋在脂质纳米盘中并处于内向开放apo 构象的马 PepT1 结构。该结构表明 ECD 通过与 TM1 相互作用将 NTD 和 CTD 桥接起来。ECD 的缺失或 ECD-TM1 界面的突变会损害转运活性。这些结果表明 ECD 在 PepT1 中具有重要作用，并增强了我们对 PepT1 转运机制的理解。
