Magnetic Resonance Center (CERM), University of Florence, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy.
Consorzio Interuniversitario di Risonanze Magnetiche di Metallo Proteine, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy.
J Chem Inf Model. 2021 Feb 22;61(2):901-912. doi: 10.1021/acs.jcim.0c01139. Epub 2021 Jan 28.
ZnT8 is a human zinc(II) transporter expressed at the membrane of secretory granules where it contributes to insulin storage importing zinc ions from the cytosol. In the human population, the two most common ZnT8 variants carry an arginine (R325) or a tryptophan (W325) in position 325. The former variant has the most efficient kinetics in zinc transport and has been correlated to a higher risk of developing insulin resistance. On the contrary, the W325 variant is less active and protects against type-2-diabetes. Here, we used molecular dynamics (MD) simulations to investigate the main differences between the R325 and W325 variants in the interaction with zinc(II) ions. Our simulations suggested that the position of the metal ion within the transport site was not the same for the two variants, underlying a different rearrangement of the transmembrane (TM) helices in the channel. The W325 variant featured a peculiar zinc environment not detected in the experimental structures. With respect to conformational dynamics, we observed that the R325 variant was significantly more flexible than W325, with the main role played by the transmembrane domain (TMD) and the C-terminal domain (CTD). This dynamics affected the packing of the TM helices and thus the channel accessibility from the cytosol. The dimer interface that keeps the two TM channels in contact became looser in both variants upon zinc binding to the transport site, suggesting that this may be an important step toward the switch from the inward- to the outward-facing state of the protein.
锌转运蛋白 8（ZnT8）是一种在分泌颗粒膜上表达的人类锌(II)转运体，它通过将锌离子从细胞质中导入来促进胰岛素储存。在人类群体中，最常见的两种 ZnT8 变体在 325 位携带精氨酸（R325）或色氨酸（W325）。前者变体在锌转运中具有最有效的动力学特性，并且与发展胰岛素抵抗的风险增加相关。相反，W325 变体的活性较低，可预防 2 型糖尿病。在这里，我们使用分子动力学（MD）模拟来研究 R325 和 W325 变体与锌(II)离子相互作用的主要差异。我们的模拟表明，金属离子在转运部位的位置在两种变体中并不相同，这表明跨膜（TM）螺旋在通道中的排列方式不同。W325 变体具有在实验结构中未检测到的特殊锌环境。关于构象动力学，我们观察到 R325 变体比 W325 变体具有更高的灵活性，主要由跨膜域（TMD）和 C 末端域（CTD）发挥作用。这种动力学影响 TM 螺旋的组装，从而影响从细胞质进入通道的通道可及性。锌结合到转运部位后，两个 TM 通道之间保持接触的二聚体界面在两种变体中变得更加宽松，这表明这可能是蛋白质从内向状态向外向状态转变的重要步骤。
