Titus Amber R, Ridgway Ellyse N, Douglas Rebecca, Brenes Elena Sánchez, Mann Elizabeth K, Kooijman Edgar E
Department of Biological Sciences, Kent State University, Kent, OH 44242, USA.
Escuela de Física, Universidad de Costa Rica, San José 11501, Costa Rica.
Membranes (Basel). 2021 Apr 6;11(4):265. doi: 10.3390/membranes11040265.
Lipid droplets (LDs) are ubiquitously expressed organelles; the only intracellular organelles that contain a lipid monolayer rather than a bilayer. Proteins localize and bind to this monolayer as they do to intracellular lipid bilayers. The mechanism by which cytosolic LD binding proteins recognize, and bind, to this lipid interface remains poorly understood. Amphipathic α-helix bundles form a common motif that is shared between cytosolic LD binding proteins (e.g., perilipins 2, 3, and 5) and apolipoproteins, such as apoE and apoLp-III, found on lipoprotein particles. Here, we use pendant drop tensiometry to expand our previous work on the C-terminal α-helix bundle of perilipin 3 and the full-length protein. We measure the recruitment and insertion of perilipin 3 at mixed lipid monolayers at an aqueous-phospholipid-oil interface. We find that, compared to its C-terminus alone, the full-length perilipin 3 has a higher affinity for both a neat oil/aqueous interface and a phosphatidylcholine (PC) coated oil/aqueous interface. Both the full-length protein and the C-terminus show significantly more insertion into a fully unsaturated PC monolayer, contrary to our previous results at the air-aqueous interface. Additionally, the C-terminus shows a preference for lipid monolayers containing phosphatidylethanolamine (PE), whereas the full-length protein does not. These results strongly support a model whereby both the N-terminal 11-mer repeat region and C-terminal amphipathic α-helix bundle domains of perilipin 3 have distinct lipid binding, and potentially biological roles.
脂滴（LDs）是普遍存在的细胞器；是唯一含有单层脂质而非双层脂质的细胞内细胞器。蛋白质定位于并结合到这个单层脂质上，就如同它们结合到细胞内脂质双层一样。胞质脂滴结合蛋白识别并结合到这个脂质界面的机制仍知之甚少。两亲性α-螺旋束形成了一种常见基序，这种基序在胞质脂滴结合蛋白（如围脂滴蛋白2、3和5）和脂蛋白颗粒上发现的载脂蛋白（如载脂蛋白E和载脂蛋白Lp-III）之间是共有的。在此，我们使用悬滴张力测定法扩展我们之前关于围脂滴蛋白3的C末端α-螺旋束和全长蛋白的研究。我们测量了围脂滴蛋白3在水-磷脂-油界面的混合脂质单层中的募集和插入情况。我们发现，与单独的C末端相比，全长围脂滴蛋白3对纯油/水界面和磷脂酰胆碱（PC）包被的油/水界面都具有更高的亲和力。与我们之前在气-水界面的结果相反，全长蛋白和C末端在完全不饱和的PC单层中都显示出明显更多的插入。此外，C末端表现出对含有磷脂酰乙醇胺（PE）的脂质单层的偏好，而全长蛋白则没有。这些结果有力地支持了一个模型，即围脂滴蛋白3的N末端11聚体重复区域和C末端两亲性α-螺旋束结构域都具有独特的脂质结合以及潜在的生物学作用。
