Oliveira Joana S L, Brezesinski Gerald, Hill Alexandra, Gericke Arne
Max Planck Institute of Colloids and Interfaces, Colloid Chemistry Department, Wissenschaftspark Potsdam-Golm, Am Mühlenberg 1, 14476 Potsdam, Germany.
Department of Biological Sciences, Kent State University, Kent, Ohio 44242, USA.
Beilstein J Nanotechnol. 2016 Feb 12;7:236-45. doi: 10.3762/bjnano.7.22. eCollection 2016.
Ceramide-1-phosphate (C1P) plays an important role in several biological processes, being identified as a key regulator of many protein functions. For instance, it acts as a mediator of inflammatory responses. The mediation of the inflammation process happens due to the interaction of C1P with the C2 domain of cPLA2α, an effector protein that needs the presence of submicromolar concentrations of calcium ions. The aim of this study was to determine the phase behaviour and structural properties of C1P in the presence and absence of millimolar quantities of calcium in a well-defined pH environment. For that purpose, we used monomolecular films of C1P at the soft air/liquid interface with calcium ions in the subphase. The pH was varied to change the protonation degree of the C1P head group. We used surface pressure versus molecular area isotherms coupled with other monolayer techniques as Brewster angle microscopy (BAM), infrared reflection-absorption spectroscopy (IRRAS) and grazing incidence X-ray diffraction (GIXD). The isotherms indicate that C1P monolayers are in a condensed state in the presence of calcium ions, regardless of the pH. At higher pH without calcium ions, the monolayer is in a liquid-expanded state due to repulsion between the negatively charged phosphate groups of the C1P molecules. When divalent calcium ions are added, they are able to bridge the highly charged phosphate groups, enhancing the regular arrangement of the head groups. Similar solidification of the monolayer structure can be seen in the presence of a 150 times larger concentration of monovalent sodium ions. Therefore, calcium ions have clearly a strong affinity for the phosphomonoester of C1P.
神经酰胺-1-磷酸（C1P）在多个生物学过程中发挥着重要作用，被认为是许多蛋白质功能的关键调节因子。例如，它作为炎症反应的介质。炎症过程的介导是由于C1P与cPLA2α的C2结构域相互作用，cPLA2α是一种效应蛋白，需要亚微摩尔浓度的钙离子存在。本研究的目的是在明确的pH环境中，测定存在和不存在毫摩尔量钙时C1P的相行为和结构性质。为此，我们使用了C1P在软空气/液体界面的单分子膜，亚相中含有钙离子。通过改变pH来改变C1P头部基团的质子化程度。我们使用表面压力与分子面积等温线，并结合其他单分子层技术，如布鲁斯特角显微镜（BAM）、红外反射吸收光谱（IRRAS）和掠入射X射线衍射（GIXD）。等温线表明，无论pH如何，在存在钙离子的情况下，C1P单分子层处于凝聚态。在没有钙离子的较高pH下，由于C1P分子带负电荷的磷酸基团之间的排斥作用，单分子层处于液体膨胀态。当加入二价钙离子时，它们能够桥接高电荷的磷酸基团，增强头部基团的规则排列。在存在浓度大150倍的单价钠离子的情况下，也可以看到单分子层结构的类似固化。因此，钙离子对C1P的磷酸单酯具有明显的强亲和力。
