Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC, UNC-CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA, Córdoba, República Argentina.
J Phys Chem B. 2010 Nov 25;114(46):15141-50. doi: 10.1021/jp104035z. Epub 2010 Oct 28.
Avian liver bile acid-binding protein (L-BABP) binds peripherically to anionic lipid membranes. We previously showed that in the absence of added salt the binding to 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) occurs with changes in the secondary structure, the extent of which depends on the phase state of the lipid. In the present work, we used Fourier transform infrared spectroscopy to study the conformations of L-BABP bound to lipids with phosphoglycerol and phosphatidic acid polar head groups and with different transition temperatures in an aqueous medium with high ionic strength (0.1 M NaCl). When L-BABP was bound to the lipids with saturated acyl chains, DMPG, 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG), 1,2-dimyristoyl-sn-glycero-3-phosphate (DMPA), and 1,2-dilauroyl-sn-glycero-3-phosphate (DLPA), the conformation shifted from a native-like secondary structure to an unfolded state at the temperature of lipid chain melting. The protein was in the native-like conformation when it was bound to the unsaturated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) in the liquid-crystalline phase. We also measured the electrokinetic surface potential of POPG and DMPG vesicles in the gel and in the liquid-crystalline phase and the protein binding constant to these lipid membranes. We found a correlation indicating that protein unfolding in the interface was due to the increase in the electrostatic surface potential that occurs in the lipid phase transition.
禽类肝脏胆堿结合蛋白（L-BABP）外周结合阴离子脂质膜。我们之前的研究表明，在没有添加盐的情况下，与 1,2-二肉豆蔻酰基-sn-甘油-3-磷酸甘油（DMPG）的结合会导致二级结构发生变化，其程度取决于脂质的相态。在本工作中，我们使用傅里叶变换红外光谱研究了在高离子强度（0.1 M NaCl）的水介质中，与具有磷酸甘油和磷脂酸极性头基以及不同相变温度的脂质结合的 L-BABP 的构象。当 L-BABP 与具有饱和酰基链的脂质结合时，DMPG、1,2-二棕榈酰基-sn-甘油-3-磷酸甘油（DPPG）、1,2-二肉豆蔻酰基-sn-甘油-3-磷酸（DMPA）和 1,2-二月桂酰基-sn-甘油-3-磷酸（DLPA），构象在脂质链熔化温度下从类似天然的二级结构转变为展开状态。当 L-BABP 与处于液晶相的不饱和 1-棕榈酰基-2-油酰基-sn-甘油-3-磷酸甘油（POPG）结合时，蛋白质处于类似天然的构象。我们还测量了凝胶相和液晶相中的 POPG 和 DMPG 囊泡的电动表面电位以及蛋白质与这些脂质膜的结合常数。我们发现了一个相关性，表明界面中蛋白质的展开是由于脂质相变过程中静电表面电位的增加所致。
