Ozturk Tugba N, Culham Doreen E, Tempelhagen Laura, Wood Janet M, Lamoureux Guillaume
Department of Physics, Concordia University, Montreal QC H4B 1R6, Canada.
Centre for Research in Molecular Modeling, Concordia University, Montreal, Quebec H4B 1R6, Canada.
J Phys Chem B. 2020 Sep 24;124(38):8209-8220. doi: 10.1021/acs.jpcb.0c03935. Epub 2020 Sep 9.
Osmosensing transporter ProP detects the increase in cytoplasmic cation concentration associated with osmotically induced cell dehydration and mediates osmolyte uptake into bacteria. ProP is a 12-transmembrane helix protein with an α-helical, cytoplasmic C-terminal domain (CTD) linked to transmembrane helix XII (TM XII). It has been proposed that the CTD helix associates with the anionic membrane surface to lock ProP in an inactive conformation and that the release of the CTD may activate ProP. To investigate this possible activation mechanism, we have built and simulated a structural model in which the CTD was anchored to the membrane by TM XII and the CTD helix was associated with the membrane surface. Molecular dynamics simulations showed specific intrapeptide salt bridges forming when the CTD associated with the membrane. Experiments supported the presence of the salt bridge Lys447-Asp455 and suggested a role for these residues in osmosensing. Simulations performed at different salt concentrations showed weakened CTD-lipid interactions at 0.25 M KCl and gradual stiffening of the membrane with increasing salinity. These results suggest that salt cations may affect CTD release and activate ProP by increasing the order of membrane phospholipids.
渗透压感应转运蛋白ProP可检测与渗透诱导的细胞脱水相关的细胞质阳离子浓度增加，并介导渗透溶质摄入细菌。ProP是一种具有12个跨膜螺旋的蛋白质，其α螺旋细胞质C末端结构域（CTD）与跨膜螺旋XII（TM XII）相连。有人提出，CTD螺旋与阴离子膜表面结合，将ProP锁定在无活性构象，而CTD的释放可能会激活ProP。为了研究这种可能的激活机制，我们构建并模拟了一个结构模型，其中CTD通过TM XII锚定在膜上，且CTD螺旋与膜表面结合。分子动力学模拟表明，当CTD与膜结合时会形成特定的肽内盐桥。实验证实了盐桥Lys447-Asp455的存在，并表明这些残基在渗透压感应中起作用。在不同盐浓度下进行的模拟显示，在0.25 M KCl时CTD与脂质的相互作用减弱，且随着盐度增加膜逐渐变硬。这些结果表明，盐阳离子可能通过增加膜磷脂的有序性来影响CTD的释放并激活ProP。
