Functional cavity dimensions of tear lipocalin
Functional cavity dimensions of tear lipocalin
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DOI：
10.1076/ceyr.21.4.824.5551
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发表时间：
2000-01-01
影响因子：
2
通讯作者：
Glasgow, BJ
中科院分区：
文献类型：
--
作者：
Abduragimov, AR;Gasymov, OK;Glasgow, BJ
目的。我们用一系列链长变长、直径变大的荧光标记脂质来校准泪液脂质体的空腔。用竞争荧光法测定空腔长度，用C12-C24中碳链长度增加的配体取代载泪脂钙蛋白中的DAUDA。比较了抑制50% DAUDA结合的竞争对手浓度（IC50）。用带有不同直径荧光标记的脂肪酸来估计眼泪脂钙蛋白和-乳球蛋白的功能直径。其他脂质体的空腔尺寸由其已发表的晶体结构坐标得到。在泪液脂钙蛋白中，脂肪酸的结合亲和增加到碳链长度为18（22.5埃），但在C18-C24之间保持不变。其他脂钙蛋白在晶体形态下的空腔长度与溶液中的撕裂脂钙蛋白相似。随着配体环尺寸的逐渐增大，泪脂钙蛋白的结合亲和力逐渐降低。与β -乳球蛋白和视黄醇结合蛋白相反，泪液脂钙蛋白结合了花萼中的dada和胆固醇。脂钙蛋白和-乳球蛋白都不能在它们各自的腔内结合P646。计算得到的脂钙蛋白结晶口的片间距离为16 ~ 22埃。由于具有更大的功能直径，泪脂钙蛋白比-乳球蛋白或视黄醇结合蛋白更混杂。不同脂钙素配体特异性的差异不能简单地用晶体结构决定的腔长或萼口片间距离的变化来解释。其他因素也可能影响配体的特异性，如-链之间环的大小和/或动态运动。
Purpose. We calibrated the cavity of tear lipocalin with a series of fluorescent labeled lipids of increasing chain length and varying diameter.Methods. Cavity length was assessed with competitive fluorescent assays in which DAUDA was displaced from apo-tear lipocalin with ligands of increasing carbon chain lengths from C12-C24. The concentrations of competitors that inhibit 50% of the binding of DAUDA (IC50) were compared. Functional diameters of tear lipocalin and beta -lactoglobulin were estimated with fatty acids bearing fluorescent labels of various diameters. The cavity dimensions of other lipocalins were derived from their published crystal structure coordinates.Results. In tear lipocalin, the binding affinities of fatty acids increased up to a carbon chain length of 18 (22.5 Angstrom) but remained constant from C18-C24. The cavity length of other lipocalins in crystal form were similar to tear lipocalin in solution. Tear lipocalin showed decreased binding affinities with progressively increasing ring dimensions of the ligand. In contrast to beta -lactoglobulin and retinol binding protein, tear lipocalin bound DAUDA and cholesterol in the calyx. Neither tear lipocalin nor beta -lactoglobulin bound P646 in their respective cavities. The calculated inter-sheet distances at the mouth of the crystallized lipocalins ranged from 16-22 Angstrom.Conclusions. Tear lipocalin is more promiscuous than beta -lactoglobulin or retinol binding protein because of a greater functional diameter. Differences in ligand specificity of the various lipocalins can not be explained simply by variation in cavity length or the inter-sheet distances at the calyx mouths as determined by crystal structure. Other factors may influence ligand specificity such as size and/or dynamic motion of loops between the beta strands.