Vaccaro A M, Tatti M, Ciaffoni F, Salvioli R, Serafino A, Barca A
Department of Metabolism and Pathological Biochemistry, Istituto Superiore Sanità, Roma, Italy.
FEBS Lett. 1994 Aug 1;349(2):181-6. doi: 10.1016/0014-5793(94)00659-8.
We have previously shown that saposin C (Sap C), a glucosylceramidase activator protein, interacts with phosphatidylserine (PS) large unilamellar vesicles (LUV), promoting the glucosylceramidase binding to the bilayer [(1993) FEBS Lett. 336, 159-162]. In the present paper the consequences of the Sap C interaction on the lipid organization of the vesicles are reported. It was found that Sap C perturbs the PS bilayer as shown by the release of an encapsulated fluorescent dye. Three different procedures, resonance energy transfer, gel filtration and electron microscopy, indicated that the activator protein is also able to make PS liposomes fuse. The effects of Sap C on PS vesicles were observed at low but not at neutral pH. The lipid composition of the bilayer also affected the Sap C-induced destabilization; in fact, the presence of PS in mixed LUV was essential for significant leakage to occur. These results demonstrate for the first time that Sap C is a protein capable of destabilizing and fusing acidic phospholipid-containing membranes in a pH-dependent fashion.
我们之前已经表明，鞘脂激活蛋白C（Sap C）与磷脂酰丝氨酸（PS）大单层囊泡（LUV）相互作用，促进葡糖神经酰胺酶与双层膜结合[（1993年）《欧洲生物化学学会联合会快报》336卷，第159 - 162页]。在本文中，报道了Sap C相互作用对囊泡脂质组织的影响。结果发现，如通过释放包封的荧光染料所示，Sap C扰乱了PS双层膜。三种不同的方法，即共振能量转移、凝胶过滤和电子显微镜，表明激活蛋白也能够使PS脂质体融合。在低pH而非中性pH条件下观察到Sap C对PS囊泡的影响。双层膜的脂质组成也影响Sap C诱导的去稳定化；事实上，混合LUV中PS的存在对于显著渗漏的发生至关重要。这些结果首次证明Sap C是一种能够以pH依赖方式使含酸性磷脂的膜去稳定化并融合的蛋白质。
