Denisov Ilia G, McLean Mark A, Shaw Andrew W, Grinkova Yelena V, Sligar Stephen G
Departments of Biochemistry and Chemistry, College of Medicine, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, 505 South Goodwin Avenue, Urbana, Illinois 61801, USA.
J Phys Chem B. 2005 Aug 18;109(32):15580-8. doi: 10.1021/jp051385g.
The role of lipid domain size and protein-lipid interfaces in the thermotropic phase transition of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) bilayers in Nanodiscs was studied using small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and generalized polarization (GP) of the lipophilic probe Laurdan. Nanodiscs are water-soluble, monodisperse, self-assembled lipid bilayers encompassed by a helical membrane scaffold protein (MSP). MSPs of different lengths were used to define the diameter of the Nanodisc lipid bilayer from 76 to 108 A and the number of DPPC molecules from 164 to 335 per discoidal structure. In Nanodiscs of all sizes, the phase transitions were broader and shifted to higher temperatures relative to those observed in vesicle preparations. The size dependences of the transition enthalpies and structural parameters of Nanodiscs reveal the presence of a boundary lipid layer in contact with the scaffold protein encircling the perimeter of the disc. The thickness of this annular layer was estimated to be approximately 15 A, or two lipid molecules. SAXS was used to measure the lateral thermal expansion of Nanodiscs, and a steep decrease of bilayer thickness during the main lipid phase transition was observed. These results provide the basis for the quantitative understanding of cooperative phase transitions in membrane bilayers in confined geometries at the nanoscale.
利用小角X射线散射（SAXS）、差示扫描量热法（DSC）以及亲脂性探针Laurdan的广义极化（GP），研究了纳米圆盘（Nanodiscs）中二棕榈酰磷脂酰胆碱（DPPC）和二肉豆蔻酰磷脂酰胆碱（DMPC）双层膜的脂质域大小和蛋白质 - 脂质界面在热致相变中的作用。纳米圆盘是由螺旋膜支架蛋白（MSP）包围的水溶性、单分散、自组装脂质双层膜。使用不同长度的MSP来定义纳米圆盘脂质双层膜的直径为76至108埃，每个盘状结构中DPPC分子的数量为164至335个。在所有尺寸的纳米圆盘中，相对于在囊泡制剂中观察到的相变，相变更宽且向更高温度偏移。纳米圆盘的转变焓和结构参数的尺寸依赖性揭示了存在与围绕圆盘周边的支架蛋白接触的边界脂质层。该环形层的厚度估计约为15埃，即两个脂质分子。SAXS用于测量纳米圆盘的横向热膨胀，并且在主要脂质相变期间观察到双层膜厚度急剧下降。这些结果为在纳米尺度的受限几何结构中定量理解膜双层中的协同相变提供了基础。
