DOPE、DOPC对重组去脂肌质网Ca~(2+)-ATPase活力和构象的影响

经磷脂酶Ａ２ 去脂的肌质网Ｃａ２ ＋ － ＡＴＰａｓｅ 重组于不同比例的二油酰磷脂酰胆碱（Ｄｉｏｌｅｏｙｌｐｈｏｐｈａｔｉｄｙｌｃｈｏｌｉｎｅ,ＤＯＰＣ） 和二油酰磷脂酰乙醇胺（Ｄｉｏｌｅｏｙｌｐｈｏｐｈａｔｉｄｙｌｅｔｈａｎｏｌａｍｉｎｅ,ＤＯＰＥ） 形成脂酶体,研究了不同磷脂环境中Ｃａ２ ＋ － ＡＴＰａｓｅ 的ＡＴＰ 水解和Ｃａ２ ＋ 转运活力。结果表明,ＤＯＰＣ 和ＤＯＰＥ 分别有利于ＡＴＰ 水解和Ｃａ２ ＋ 的转运,ＤＯＰＥ 可以增强Ｃａ２ ＋ － ＡＴＰａｓｅ 的ＡＴＰ水解和Ｃａ２ ＋ 转运之间的偶联效率。利用内源荧光、荧光淬灭及Ｆｏｒｓｔｅｒ 能量转移原理测定Ｃａ２ ＋ －ＡＴＰａｓｅ 相应的构象变化, 发现随着ＤＯＰＥ／ ＤＯＰＣ 比例的改变使Ｃａ２ ＋ － ＡＴＰａｓｅ 构象发生相应的变化。     

Three dimensional (temperature–tension–composition) phase map of mixed DOPC–DPPC vesicles: Two solid phases and a fluid phase coexist on three intersecting planes

Mapping the phase behavior of multicomponent phospholipid membranes has been an ongoing pursuit, motivated by interest in both fundamental physics and cell function. Prior investigations addressed temperature-composition space and the features of the associated domains. The current study additionally considers membrane tension, analogous to pressure in bulk materials. Focusing on model mixed 1,2-dioleoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DOPC and DPPC respectively) membranes, we examine the thermodynamic impact of tension on fluid-solid coexistence and the nature of phase-separated domains. Reported here is the 3 dimensional composition-temperature-tension phase map containing three intersecting curved surfaces. Depending on the system’s position in this 3D space, giant unilamellar vesicles containing DOPC and DPPC may exhibit, in addition to a 2-component fluid Lα phase, two different types of solid DPPC-rich domains: tracer-excluding hexagonal patches or tracer-selective stripes. The fluid phase occurs at high temperatures. At cool temperatures striped solid DPPC-rich domains coexist with the fluid at elevated tensions. These stripes occur independent of tension, at the coolest temperatures. At low tensions and intermediate temperatures, patchy solid DPPC-rich domains coexist with the Lα fluid and may persist, if kinetically trapped, at lower temperatures. We associate the striped DPPC domains with a tilt-gel (Lβ’) morphology and the hexagonal DPPC patches with a dense corrugated ripple phase (Pβ’). These assignments, based on the reported areal densities of the corrugated and tilt solids, enabled first principles estimates of the coexistence boundaries that match the experiments well, including the tension sensitivity of coexistence curves and triple-point-like features for fixed composition.