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Proc Natl Acad Sci U S A. 2017 Aug 1;114(31):8259-8264. doi: 10.1073/pnas.1704725114. Epub 2017 Jul 14.

Subunit conformational variation within individual GroEL oligomers resolved by Cryo-EM.

Author information

1
National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030.
2
Graduate Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, TX 77030.
3
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030.
4
Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742.
5
National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030; wah@bcm.edu.

Abstract

Single-particle electron cryo-microscopy (cryo-EM) is an emerging tool for resolving structures of conformationally heterogeneous particles; however, each structure is derived from an average of many particles with presumed identical conformations. We used a 3.5-Å cryo-EM reconstruction with imposed D7 symmetry to further analyze structural heterogeneity among chemically identical subunits in each GroEL oligomer. Focused classification of the 14 subunits in each oligomer revealed three dominant classes of subunit conformations. Each class resembled a distinct GroEL crystal structure in the Protein Data Bank. The conformational differences stem from the orientations of the apical domain. We mapped each conformation class to its subunit locations within each GroEL oligomer in our dataset. The spatial distributions of each conformation class differed among oligomers, and most oligomers contained 10-12 subunits of the three dominant conformation classes. Adjacent subunits were found to more likely assume the same conformation class, suggesting correlation among subunits in the oligomer. This study demonstrates the utility of cryo-EM in revealing structure dynamics within a single protein oligomer.

KEYWORDS:

atomic-model per-particle; chaperonin; conformational variation; cryo-EM; focused classification

PMID:
28710336
PMCID:
PMC5547627
DOI:
10.1073/pnas.1704725114
[Indexed for MEDLINE]
Free PMC Article

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