Schmid M F, Sherman M B, Matsudaira P, Tsuruta H, Chiu W
Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
J Struct Biol. 1999 Dec 1;128(1):51-7. doi: 10.1006/jsbi.1999.4173.
The structure factors derived from electron cryomicroscopic images are modified by the contrast transfer function of the microscope's objective lens and other influences. The phases of the structure factors can be corrected in a straightforward way when the positions of the contrast transfer function rings are determined. However, corrected amplitudes are also essential to yield an accurate distribution of mass in the reconstruction. The correct scale factors for the amplitudes are difficult to evaluate for data that are merged from many different micrographs. We opt to use X-ray solution scattering intensity from a concentrated suspension of the specimen to correct the amplitudes of the spherically averaged structure factors. When this approach is applied to the three-dimensional image data of ice-embedded acrosomal bundles, the core of a filament in a three-dimensional reconstruction of the acrosomal bundle becomes denser and matches more closely the outer density ascribed to scruin.
从电子冷冻显微镜图像中导出的结构因子会受到显微镜物镜的对比度传递函数及其他因素的影响。当确定对比度传递函数环的位置时，结构因子的相位可以直接校正。然而，校正后的振幅对于在重建中获得准确的质量分布也至关重要。对于从许多不同显微照片合并的数据，很难评估振幅的正确比例因子。我们选择使用来自标本浓缩悬浮液的X射线溶液散射强度来校正球平均结构因子的振幅。当将这种方法应用于冰包埋顶体束的三维图像数据时，顶体束三维重建中细丝的核心变得更密集，并且与归因于丝氨酸蛋白酶的外部密度更紧密匹配。
