Cheng Kwan Hon, Cannon Brian, Metze Jennifer, Lewis Anthony, Huang Juyang, Vaughn Mark W, Zhu Qing, Somerharju Pentti, Virtanen Jorma
Department of Physics, Texas Tech University, Lubbock, Texas 79409, USA.
Biochemistry. 2006 Sep 12;45(36):10855-64. doi: 10.1021/bi060937y.
The relationship between the molecular organization of lipid headgroups and the activity of surface-acting enzyme was examined using a bacterial cholesterol oxidase (COD) as a model. The initial rate of cholesterol oxidation by COD in fluid state 1-palmitoyl-2-oleoyl-phosphatidylethanolamine/1-palmitoyl-2-oleoyl-phosphatidylcholine/cholesterol (POPE/POPC/CHOL) bilayers was measured as a function of POPE-to-phospholipid mole ratio (X(PE)) and cholesterol-to-lipid mole ratio (X(CHOL)) at 37 degrees C. At X(PE) = 0, the COD activity changed abruptly at X(CHOL) approximately 0.40, whereas major activity peaks were detected at X(PE) approximately 0.18, 0.32, 0.50, 0.64, and 0.73 when X(CHOL) was fixed to 0.33 or 0.40. At a fixed X(CHOL) of 0.50, the COD activity increased progressively with PE content and exhibited small peaks or kinks at X(PE) approximately 0.40, 0.50, 0.58, 0.69, and 0.81. When X(PE) and X(CHOL) were systematically varied within a narrow 2-D lipid composition window, an onset of COD activity at X(CHOL) approximately 0.40 and the elimination of the activity peak at X(PE) approximately 0.64 for X(CHOL) >0.40 were clearly observed. Except for X(PE) approximately 0.40 and 0.58, the observed critical PE mole ratios agree closely (+/-0.03) with those predicted by a headgroup superlattice model (Virtanen, J.A., et al. (1998) Proc. Natl. Acad. Sci. U.S.A. 95, 4964-4969; Cannon, B., et al. (2006) J. Phys. Chem. B 110, 6339-6350), which proposes that lipids with headgroups of different sizes tend to adopt regular, superlattice-like distributions at discrete and predictable compositions in fluid lipid bilayers. Our results indicate that headgroup superlattice domains exist in lipid bilayers and that they may play a crucial role in modulating the activity of enzymes acting on the cell membrane surface.
以细菌胆固醇氧化酶（COD）为模型，研究了脂质头部基团的分子组织与表面活性酶活性之间的关系。在37℃下，测量了COD在液态1-棕榈酰-2-油酰磷脂酰乙醇胺/1-棕榈酰-2-油酰磷脂酰胆碱/胆固醇（POPE/POPC/CHOL）双层膜中氧化胆固醇的初始速率，该速率是POPE与磷脂摩尔比（X(PE)）和胆固醇与脂质摩尔比（X(CHOL)）的函数。当X(PE)=0时，COD活性在X(CHOL)约为0.40时突然变化，而当X(CHOL)固定为0.33或0.40时，在X(PE)约为0.18、0.32、0.50、0.64和0.73处检测到主要活性峰。在固定的X(CHOL)为0.50时，COD活性随PE含量逐渐增加，并在X(PE)约为0.40、0.50、0.58、0.69和0.81处出现小峰或拐点。当X(PE)和X(CHOL)在狭窄的二维脂质组成窗口内系统变化时，清楚地观察到在X(CHOL)约为0.40时COD活性开始出现，并且当X(CHOL)>0.40时，在X(PE)约为0.64处的活性峰消失。除了X(PE)约为0.40和0.58外，观察到的临界PE摩尔比与头部基团超晶格模型预测的结果（Virtanen, J.A.,等人（1998年）《美国国家科学院院刊》95, 4964 - 4969；Cannon, B.,等人（2006年）《物理化学杂志B》110, 6339 - 6350）非常吻合（±0.03），该模型提出具有不同大小头部基团的脂质倾向于在流体脂质双层膜中以离散且可预测的组成采用规则的、超晶格状分布。我们的结果表明，头部基团超晶格域存在于脂质双层膜中，并且它们可能在调节作用于细胞膜表面的酶的活性方面发挥关键作用。
