Classification and Reconstruction of a Heterogeneous Set of Electron Microscopic Images: A Case Study of GroEL–Substrate Complexes

• Published in: Journal of structural biology 2001-02, Vol.133 (2-3), p.203-213
• Main Authors: Falke, Scott, Fisher, Mark T., Gogol, Edward P.
• Format: Article
• Language: English
• Subjects: chaperonin; Chaperonin 60 - chemistry; Chaperonin 60 - metabolism; Cryoelectron Microscopy - methods; electron microscopy; Escherichia coli - chemistry; Glutamate-Ammonia Ligase - chemistry; Glutamate-Ammonia Ligase - metabolism; GroEL; Image Processing, Computer-Assisted - methods; image reconstruction; Imaging, Three-Dimensional; Macromolecular Substances; Models, Molecular; Protein Binding; Protein Conformation
• ISSN: 1047-8477; 1095-8657
• DOI: 10.1006/jsbi.2001.4354

Image analysis methods were used to separate images of a large macromolecular complex, the chaperonin GroEL, in a preparation in which it is partially liganded to a nonnative protein substrate, glutamine synthetase. The relatively small difference (∼6%) in size between the chaperonin in its free and complexed forms, and the absence of gross changes in overall conformation, made separation of the two types of particles challenging. Different approaches were evaluated and used for alignment and classification of images, both in two common projections and in three dimensions, yielding 2D averages and a 3D reconstruction. The results of 3D analysis describe the conformational changes effected by binding of this particular protein substrate and demonstrate the utility of 2D analysis as an indicator of structural change in this system.