Loura Luís M S, do Canto António M T Martins, Martins Jorge
Universidade de Coimbra, Pólo das Ciências da Saúde, Azinhaga de Santa Comba, Coimbra, Portugal.
Biochim Biophys Acta. 2013 Mar;1828(3):1094-101. doi: 10.1016/j.bbamem.2012.12.014. Epub 2012 Dec 26.
Molecular dynamics (MD) simulations of bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with varying amounts of cholesterol (0, 5, 20, and 40mol%) were carried out in the absence and presence of inserted pyrene molecules. Both fluorophore and bilayer parameters were computed, for characterization of probe location and dynamics, as well as its effects on the host bilayer. In agreement with previous studies in fluid disordered bilayers, pyrene prefers to be located in the hydrophobic acyl chain region of POPC bilayers, close to the glycerol group of lipid molecules and causes ordering of the lipid acyl chains. However, incorporation of pyrene in binary POPC/cholesterol bilayers decreases the acyl chain order parameter (especially near the end of the chains), opposing the ordering effect of cholesterol. These effects are modest and mainly felt locally. Significantly, as the bilayer is enriched with cholesterol, the relative position of pyrene and the POPC carbonyl and phosphocholine groups is invariant, and the local water density around the probe decreases. This work clarifies and supports the cautious use of pyrene Ham effect to effectively measure equivalent polarity in lipid bilayers. Within the time scale of the MD simulations, which is of the magnitude of the fluorescence lifetime of pyrene, the thermally averaged polarity of lipid bilayers is nearly out of influence of spurious uncertainty in the transverse location of pyrene in the bilayers. This renders the values of equivalent polarity measurements through the pyrene Ham effect more reliable and reproducible than previously expected.
在不存在和存在插入芘分子的情况下，对含有不同胆固醇含量（0、5、20和40摩尔%）的1-棕榈酰-2-油酰基-sn-甘油-3-磷酸胆碱（POPC）双层进行了分子动力学（MD）模拟。计算了荧光团和双层参数，以表征探针的位置和动力学，以及其对主体双层的影响。与先前在流体无序双层中的研究一致，芘倾向于位于POPC双层的疏水酰基链区域，靠近脂质分子的甘油基团，并导致脂质酰基链有序排列。然而，在二元POPC/胆固醇双层中掺入芘会降低酰基链序参数（尤其是在链的末端附近），这与胆固醇的有序化作用相反。这些影响较小，主要在局部感受到。值得注意的是，随着双层中胆固醇含量的增加，芘与POPC羰基和磷酸胆碱基团的相对位置不变，并且探针周围的局部水密度降低。这项工作阐明并支持谨慎使用芘Ham效应来有效测量脂质双层中的等效极性。在MD模拟的时间尺度内，即芘荧光寿命的量级，脂质双层的热平均极性几乎不受芘在双层中横向位置的虚假不确定性的影响。这使得通过芘Ham效应进行的等效极性测量值比以前预期的更可靠和可重复。
