Departments of Ophthalmology, Pathology and Laboratory Medicine, Jules Stein Eye Institute, 100 Stein Plaza, University of California, Los Angeles, CA, 90095, USA.
Biochem Biophys Res Commun. 2021 Apr 9;548:35-38. doi: 10.1016/j.bbrc.2021.02.054. Epub 2021 Feb 22.
Phospholipid transfer protein, ∼80 kDa, transfers phospholipids from micelles to lipid binding proteins. The acceptor protein in plasma is apolipoprotein-A1, 28 kDa. Previously, phospholipid transfer protein was found in tears but an acceptor protein was not identified. To search for the acceptor protein(s) in tears a fluorescent phospholipid transfer assay was altered to omit the extrinsic acceptor. Human tears were incubated with fluorescent micelles and showed marked transfer activity verifying a native acceptor protein must be present. Reconstituted tears without tear lipocalin (lipocalin-1) eliminated the transfer of phospholipids. To determine if phospholipid transfer protein is involved in carrying phospholipid to the surface of tears from tear lipocalin, a fraction enriched in phospholipid transfer protein was injected into the subphase of a tear mimicking buffer in which tear lipocalin was present. The addition of phospholipid transfer protein did not increase the thickness of the surface layer regardless of the presence of lipid bearing tear lipocalin. The data show that phospholipid transfer protein transfers phospholipid from micelles to tear lipocalin. Phospholipid transfer protein does not transport the phospholipid. While tear lipocalin has no intrinsic transfer activity from micelles, it is the acceptor protein for phospholipid transfer protein in tears.
磷脂转移蛋白，约 80 kDa，将磷脂从胶束转移到脂质结合蛋白。血浆中的受体蛋白是载脂蛋白-A1，28 kDa。先前，磷脂转移蛋白在泪液中被发现，但未鉴定出受体蛋白。为了在泪液中寻找受体蛋白，荧光磷脂转移测定法进行了修改，省略了外源性受体。用人的眼泪孵育荧光胶束，显示出明显的转移活性，证实必须存在天然的受体蛋白。没有泪液乳铁蛋白（乳铁蛋白-1）的重组泪液消除了磷脂的转移。为了确定磷脂转移蛋白是否参与从泪液乳铁蛋白向泪液表面携带磷脂，将富含磷脂转移蛋白的级分注入存在泪液乳铁蛋白的模拟泪液缓冲液的亚相中。无论是否存在带有脂质的泪液乳铁蛋白，添加磷脂转移蛋白都不会增加表面层的厚度。数据表明，磷脂转移蛋白将磷脂从胶束转移到泪液乳铁蛋白。磷脂转移蛋白不会运输磷脂。虽然泪液乳铁蛋白本身没有从胶束转移的内在活性，但它是泪液中磷脂转移蛋白的受体蛋白。
