Hydrophobic ligand binding properties of the human lipocalin apolipoprotein M
Hydrophobic ligand binding properties of the human lipocalin apolipoprotein M
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DOI：
10.1194/jlr.m700103-jlr200
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发表时间：
2007-08-01
影响因子：
6.5
通讯作者：
Dahlback, Bjorn
中科院分区：
文献类型：
--
作者：
Ahnstrom, Josefin;Faber, Kirsten;Dahlback, Bjorn
载脂蛋白M （apoM）是一种主要与HDL相关的血浆蛋白。ApoM被认为对pre - hdl的形成很重要，但其作用机制尚不清楚。同源性模型表明apoM是一种脂质体。脂质钙素共享一个结构保守的β -桶，在许多脂质钙素中与疏水配体结合。本研究的目的是测试apoM结合不同疏水物质的能力。在大肠杆菌和HEK 293细胞中均可产生ApoM。用电泳和免疫学方法对这两种变异进行了表征，表明来自大肠杆菌的apoM是正确折叠的。两种apoM变体的固有色氨酸荧光显示视黄醇、全反式视黄酸和9顺式视黄酸结合（解离常数为5 2-3 μ M），而其他测试物质（如胆固醇、维生素K和花生四烯酸）没有。两个携带单一色氨酸的apoM突变体被视黄醇和视黄酸猝灭的程度与野生型apoM相同，表明两种色氨酸的结合环境都受到了影响。综上所述，视黄醇和视黄酸的结合支持了apoM是一种脂钙素的假设。这种结合的生理相关性还有待阐明。
Apolipoprotein M (apoM) is a plasma protein associated mainly with HDL. ApoM is suggested to be important for the formation of pre beta-HDL, but its mechanism of action is unknown. Homology modeling has suggested apoM to be a lipocalin. Lipocalins share a structurally conserved beta-barrel, which in many lipocalins bind hydrophobic ligands. The aim of this study was to test the ability of apoM to bind different hydrophobic substances. ApoM was produced both in Escherichia coli and in HEK 293 cells. Characterization of both variants with electrophoretic and immunological methods suggested apoM from E. coli to be correctly folded. Intrinsic tryptophan fluorescence of both apoM variants revealed that retinol, all-trans-retinoic acid, and 9-cis-retinoic acid bound ( dissociation constant 5 2-3 mu M), whereas other tested substances ( e.g., cholesterol, vitamin K, and arachidonic acid) did not. The intrinsic fluorescence of two apoM mutants carrying single tryptophans was quenched by retinol and retinoic acid to the same extent as wild-type apoM, indicating that the environment of both tryptophans was affected by the binding. In conclusion, the binding of retinol and retinoic acid supports the hypothesis that apoM is a lipocalin. The physiological relevance of this binding has yet to be elucidated.