Size and Shape of Bovine Interphotoreceptor Retinoid-binding Protein by Electron Microscopy and Hydrodynamic Analysis*
Size and Shape of Bovine Interphotoreceptor Retinoid-binding Protein by Electron Microscopy and Hydrodynamic Analysis*
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通过电子显微镜和流体动力学分析确定牛光感受器间视黄醇结合蛋白的大小和形状*
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
S.
中科院分区：
文献类型：
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作者：
J.;F.;S.
光感受器间维甲酸结合蛋白（IRBP）是一种可能在视觉周期中很重要的蛋白质，通过电子显微镜观察到其单个分子。IRBP表面涂有一层极薄的钨，并通过暗场成像拍摄。IRBP被认为是一个柔韧的细长分子，长约24 nm，宽约3-4 nm（统计模式）。这些尺寸与从沉积资料中得到的摩擦比计算结果非常吻合。这些杆状IRBP分子中大约有一半是直的，一半在中间弯曲，通常两臂之间的角度为60-90英寸。将IRBP表示为一串可弯曲的珠子，可以计算出与电子显微镜和沉降数据一致的尺寸和流体动力学参数；由这种表示得到的沉降系数对分子弯曲几乎不敏感。当IRBP与饱和量的内源性配体（全trans - 1-顺式视黄醇）结合时，其沉降行为不变，并且在电子显微镜下可以看到与游离蛋白相同类型的颗粒；然而，更大比例的分子是弯曲的。如凝胶过滤和沉淀数据所示，IRBP的去糖基化（使用肽：n -糖苷酶F）会产生一个略小的分子，并保持其棒状形状。结果表明IRBP是一个细长的分子，并提示配体结合后可能发生结构变化。
Individual molecules of interphotoreceptor retinoidbinding protein (IRBP), a protein likely to be important in the visual cycle, were visualized by means of electron microscopy. IRBP was coated with a very thin layer of tungsten and photographed by dark-field imaging. IRBP is seen to be a flexible, elongated molecule about 24 nm in length by 3-4 nm in width (statistical modes). These dimensions agree very well with those calculated from the frictional ratio obtained from sedimentation data. Approximately half of these rodshaped IRBP molecules are straight, and half are bent in the middle, usually with an angle of 60-90” between the two arms. A representation of IRBP as a bendable string of beads yields calculations of dimensions and of hydrodynamic parameters consistent with the electron microscopic and sedimentation data; the sedimentation coefficients derived from this representation are nearly insensitive to molecular bending. When IRBP is bound to saturating amounts of its endogenous ligands, all-transor 1 1-cis-retinol, its sedimentation behavior is unchanged, and the same types of particles are visualized by electron microscopy as with the free protein; however, a greater proportion of the molecules are bent. Deglycosylation of IRBP (with peptide:N-glycosidase F) results in a somewhat smaller molecule that retains its rod-like shape, as shown by gel filtration and sedimentation data. The results indicate that IRBP is an elongated molecule and suggest that a structural change may occur upon ligand binding.