NanoBioMedical Centre, Adam Mickiewicz University, Wszechnicy Piastowskiej 3, 61-614 Poznań, Poland.
Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308 Gdańsk, Poland.
Int J Mol Sci. 2019 Aug 26;20(17):4172. doi: 10.3390/ijms20174172.
The transmembrane (TM) proteins are gateways for molecular transport across the cell membrane that are often selected as potential targets for drug design. The bilitranslocase (BTL) protein facilitates the uptake of various anions, such as bilirubin, from the blood into the liver cells. As previously established, there are four hydrophobic transmembrane segments (TM1-TM4), which constitute the structure of the transmembrane channel of the BTL protein. In our previous studies, the 3D high-resolution structure of the TM2 and TM3 transmembrane fragments of the BTL in sodium dodecyl sulfate (SDS) micellar media were solved using Nuclear Magnetic Resonance (NMR) spectroscopy and molecular dynamics simulations (MD). The high-resolution 3D structure of the fourth transmembrane region (TM4) of the BTL was evaluated using NMR spectroscopy in two different micellar media, anionic SDS and zwitterionic DPC (dodecylphosphocholine). The presented experimental data revealed the existence of an α -helical conformation in the central part of the TM4 in both micellar media. In the case of SDS surfactant, the α -helical conformation is observed for the Pro258-Asn269 region. The use of the zwitterionic DPC micelle leads to the formation of an amphipathic α -helix, which is characterized by the extension of the central α -helix in the TM4 fragment to Phe257-Thr271. The complex character of the dynamic processes in the TM4 peptide within both surfactants was analyzed based on the relaxation data acquired on 15 N and 31 P isotopes. Contrary to previously published and present observations in the SDS micelle, the zwitterionic DPC environment leads to intensive low-frequency molecular dynamic processes in the TM4 fragment.
跨膜（TM）蛋白是分子跨膜运输的通道，通常被选为药物设计的潜在靶点。胆红素转运蛋白（BTL）促进各种阴离子（如胆红素）从血液进入肝细胞。如前所述，BTL 蛋白有四个疏水性跨膜结构域（TM1-TM4），它们构成了 BTL 蛋白跨膜通道的结构。在我们之前的研究中，使用核磁共振（NMR）光谱和分子动力学模拟（MD）方法，在十二烷基硫酸钠（SDS）胶束介质中解决了 BTL 的 TM2 和 TM3 跨膜片段的 3D 高分辨率结构。使用 NMR 光谱在两种不同的胶束介质（阴离子 SDS 和两性离子 DPC（十二烷基磷酸胆碱））中评估了 BTL 的第四跨膜区（TM4）的高分辨率 3D 结构。呈现的实验数据表明，在两种胶束介质中，TM4 的中心部分都存在α-螺旋构象。在 SDS 表面活性剂的情况下，观察到 Pro258-Asn269 区域的α-螺旋构象。使用两性离子 DPC 胶束会导致形成两亲性α-螺旋，其特征在于 TM4 片段的中心α-螺旋延伸到 Phe257-Thr271。根据在 15N 和 31P 同位素上获得的弛豫数据，分析了两种表面活性剂中 TM4 肽内动态过程的复杂特征。与 SDS 胶束中先前发表的和目前的观察结果相反，两性离子 DPC 环境导致 TM4 片段中密集的低频分子动力学过程。
