Biochemistry, Faculty of Science and Engineering, Åbo Akademi University, Turku, Finland.
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan.
Biophys J. 2019 Apr 23;116(8):1507-1515. doi: 10.1016/j.bpj.2019.03.004. Epub 2019 Mar 19.
Ceramide is an important intermediate in sphingolipid homeostasis. We examined how colipids, with negative intrinsic curvature and which may induce curvature stress in the bilayers, affected the segregation of palmitoyl ceramide (PCer). Such colipids include 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and tetra-linoleoyl cardiolipin (CL). In 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers, PCer formed ordered, gel-like domains at concentrations above 10 mol% at 23°C, as evidenced by the change in the average lifetime of the trans-parinaric acid emission. When POPE or DOPE were included in the DOPC bilayer (at 20:80 or 40:60 POPE or DOPE to DOPC, by mol), the lateral segregation of PCer was facilitated in a concentration-dependent manner, and less PCer was required for the formation of the ordered ceramide-rich domains. Inclusion of CL in the DOPE bilayer (at 10:90 or 20:80 CL to PC, by mol) also caused a similar facilitation of the lateral segregation of PCer. The PCer-rich domains formed in the presence of POPE, DOPE, or CL in DOPC bilayers were slightly more thermostable (by 2-10°C) when compared to PCer-rich domains in DOPC-only bilayers. Nonlamellar phases were not present in bilayers in which the effects of POPE or DOPE on PCer segregation were the largest, as verified by P NMR. When palmitoyl sphingomyelin was added to the different bilayer compositions at 5 mol%, relative to the phospholipids, PCer segregated into gel domains at lower concentrations (2-3 mol% PCer), and the effect of POPE on PCer segregation was eliminated. We suggest that the effects of POPE, DOPE, and CL on PCer segregation was in part influenced by their effects on membrane curvature stress and in part because of unfavorable interactions with PCer due to their unsaturated acyl chains. These lipids are abundant in mitochondrial membranes and are likely to affect functional properties of saturated ceramides in them.
神经酰胺是神经鞘脂代谢的关键中间产物，参与多种细胞生理功能的调节。我们研究了具有负曲率内在特性的类脂，即可能在双层膜中诱导曲率压力的类脂，如何影响棕榈酰神经酰胺（PCer）的分隔。这些类脂包括 1-棕榈酰-2-油酰基-sn-甘油-3-磷酸乙醇胺（POPE）、1,2-二油酰基-sn-甘油-3-磷酸乙醇胺（DOPE）和四油酰基心磷脂（CL）。在 1,2-二油酰基-sn-甘油-3-磷酸胆碱（DOPC）双层膜中，当浓度高于 23°C 时的 10 mol%时，PCer 形成有序的凝胶状结构，这一点可以通过 trans-parinaric 酸发射的平均寿命的变化来证明。当 POPE 或 DOPE 被包含在 DOPC 双层膜中（20：80 或 40：60 POPE 或 DOPE 与 DOPC，摩尔比）时，PCer 的横向分隔以浓度依赖的方式得到促进，并且形成有序的神经酰胺丰富的域所需的 PCer 较少。CL 被包含在 DOPE 双层膜中（10：90 或 20：80 CL 与 PC，摩尔比）也导致 PCer 横向分隔的类似促进。与仅含有 DOPC 的双层膜中的 PCer 丰富域相比，在含有 POPE、DOPE 或 CL 的 DOPC 双层膜中形成的 PCer 丰富域的热稳定性略高（高 2-10°C）。通过 P NMR 验证，在 POPE 或 DOPE 对 PCer 分隔的影响最大的双层膜中不存在非层状相。当棕榈酰鞘氨醇以相对于磷脂的 5 mol%添加到不同的双层组成中时，PCer 在较低浓度（2-3 mol% PCer）下分离到凝胶域中，并且 POPE 对 PCer 分隔的影响被消除。我们认为，POPE、DOPE 和 CL 对 PCer 分隔的影响部分受其对膜曲率压力的影响，部分受其不饱和酰基链与 PCer 之间的不利相互作用的影响。这些脂质在线粒体膜中含量丰富，可能会影响其中饱和神经酰胺的功能特性。
