Institute of Biochemistry and Molecular Medicine, and Swiss National Centre of Competence in Research (NCCR) TransCure, University of Bern, CH-3012 Bern, Switzerland.
Int J Mol Sci. 2020 Sep 25;21(19):7094. doi: 10.3390/ijms21197094.
Heterodimeric amino acid transporters (HATs) are protein complexes mediating the transport of amino acids and derivatives thereof across biological membranes. HATs are composed of two subunits, a heavy and a light chain subunit belonging to the solute carrier (SLC) families SLC3 and SLC7. The human HAT 4F2hc-LAT2 is composed of the type-II membrane N-glycoprotein 4F2hc (SCL3A2) and the L-type amino acid transporter LAT2 (SLC7A8), which are covalently linked to each other by a conserved disulfide bridge. Whereas LAT2 catalyzes substrate transport, 4F2hc is important for the successful trafficking of the transporter to the plasma membrane. The overexpression, malfunction, or absence of 4F2hc-LAT2 is associated with human diseases, and therefore, this heterodimeric complex represents a potential drug target. The recombinant human 4F2hc-LAT2 can be functionally overexpressed in the methylotrophic yeast , and the protein can be purified. Here, we present the cryo-EM density map of the human 4F2hc-LAT2 amino acid transporter at sub-nanometer resolution. A homology model of 4F2hc-LAT2 in the inward-open conformation was generated and fitted into the cryo-EM density and analyzed. In addition, disease-causing point mutations in human LAT2 were mapped on the homology model of 4F2hc-LAT2, and the possible functional implications on the molecular level are discussed.
异二聚体氨基酸转运体（HAT）是介导氨基酸及其衍生物跨生物膜转运的蛋白复合物。HAT 由两个亚基组成，一个重链亚基和一个轻链亚基，属于溶质载体（SLC）家族 SLC3 和 SLC7。人 HAT 4F2hc-LAT2 由 II 型膜 N-糖蛋白 4F2hc（SCL3A2）和 L 型氨基酸转运体 LAT2（SLC7A8）组成，它们通过保守的二硫键共价连接在一起。虽然 LAT2 催化底物转运，但 4F2hc 对于转运体成功转运到质膜至关重要。4F2hc-LAT2 的过度表达、功能障碍或缺失与人类疾病有关，因此，这种异二聚体复合物代表了一个潜在的药物靶点。重组人 4F2hc-LAT2 可以在甲基营养酵母中功能性过表达，并且可以对其进行纯化。在这里，我们呈现了人 4F2hc-LAT2 氨基酸转运体在亚纳米分辨率下的 cryo-EM 密度图。生成了 4F2hc-LAT2 的同源模型，并将其拟合到 cryo-EM 密度中进行分析。此外，还将人类 LAT2 中的致病点突变映射到 4F2hc-LAT2 的同源模型上，并讨论了它们在分子水平上可能产生的功能影响。
