Estimation of variance distribution in threedimensional reconstruction II Applications

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Abstract
A previously developed theory of three-dimensional (3-D) variance estimation [ J. Opt. Soc. Am. A 12, 2615– 2627 ( 1995)] is applied to the structural study of a hemocyanin-Fab complex with the electron microscope. The precise locations of structurally variable regions of the macromolecule are determined from the 3-D variance maps. The structural differences among different classes of the macromolecular complex are assessed by the use of the statistical t-test, and the 3-D antibody binding sites are revealed. From a model analysis, a rule is demonstrated for visually identifying a 3-D conformational change by the inspection of the 3-D variance map. Our analysis lays the foundation for numerous practical applications of variance estimation in the 3-D imaging of macromolecules.