Rost L E, Hanein D, DeRosier D J
W.M. Keck Institute for Cellular Visualization, Department of Biology, Brandeis University, Waltham, MA 02254, USA.
Ultramicroscopy. 1998 May;72(3-4):187-97. doi: 10.1016/s0304-3991(98)00017-5.
The absolute value of individual differences (AVID) procedure is a method to map variations within images arising from deviations in symmetry. We devised this procedure to analyze images of actin filaments decorated with actin-binding proteins (ABPs). In three-dimensional maps of such actin complexes, ABPs often appear weak (i.e. they have low density) relative to actin. Because the 3D map represents an average taken over equivalent positions in the helix, the final density at the position of the ABP represents an average of the densities at all ABP sites. If there is either incomplete binding or a conformational variability of the bound ABP, the average density will be lowered. By the same argument, the variation of density at these sites will be increased. The aim of the AVID procedure is to calculate the density variations within partially decorated filaments and thereby attempt to locate the bound protein. We tested the AVID procedure with model data and then applied it to electron micrographs of F-actin decorated with an actin-binding domain of fimbrin known as N375 [Hanein et al., J. Cell Biol. 139 (1997) 387-396]. The AVID maps have peaks at the site where N375 binds. Because it excludes the layer line data, the AVID procedure uses data that are independent of the data used for 3D reconstruction and difference mapping. It therefore provides an independent way to localize the bound subunit without the need for a map of undecorated actin. Moreover, the difficulties of scaling maps are minimized. This procedure could also be applied to structures with non-helical symmetry.
个体差异绝对值（AVID）程序是一种用于描绘因对称性偏差而在图像中产生的变化的方法。我们设计此程序来分析用肌动蛋白结合蛋白（ABP）修饰的肌动蛋白丝图像。在这种肌动蛋白复合物的三维图谱中，相对于肌动蛋白，ABP通常显得较弱（即它们具有低密度）。由于三维图谱表示在螺旋中等效位置上获取的平均值，ABP位置处的最终密度代表所有ABP位点密度的平均值。如果存在不完全结合或结合的ABP的构象变异性，则平均密度会降低。基于同样的道理，这些位点处的密度变化将会增加。AVID程序的目的是计算部分修饰丝内的密度变化，从而尝试定位结合的蛋白质。我们用模型数据测试了AVID程序，然后将其应用于用丝状肌动蛋白结合蛋白的肌动蛋白结合结构域N375修饰的F-肌动蛋白的电子显微照片[哈内因等人，《细胞生物学杂志》139（1997）387 - 396]。AVID图谱在N375结合的位点处有峰值。由于它排除了层线数据，AVID程序使用的是与用于三维重建和差异映射的数据无关的数据。因此，它提供了一种独立的方法来定位结合的亚基，而无需未修饰肌动蛋白的图谱。此外，图谱缩放的困难被最小化。此程序也可应用于具有非螺旋对称性的结构。
