Improved common line-based icosahedral particle image orientation estimation algorithms.

Modifications are described for the center and angular parameter estimation algorithms of common line-based particle image orientation determination which is an essential step in the three-dimensional reconstruction of icosahedral virus particles. The modifications incorporate a variety of image processing, pattern recognition, and statistical tools resulting in objective and automated orientation estimation algorithms. The modified algorithms were tested using electron cryo-microscopic particle images of three different virus specimens, with sizes 400-1250 A in diameter, covering a broad range of defocus values. Evaluation of these modified algorithms shows significant improvement over the previous algorithms. The center and angular parameters were estimated with higher accuracy allowing the identification of a larger number of particle orientations. Usage of the modified estimation algorithms resulted in the identification of particle orientations which could not to be identified using the algorithms before modification. Furthermore, these improvements have resulted in the determination of a better quality and a higher resolution three-dimensional reconstruction. The improved algorithms have been developed into a software package which can be obtained via the world wide web at http://ncmi.bioch.bcm.tmc.edu/pthuman.