Abstract
The chaperonins (GroEL and GroES in Escherichia coli) are ubiquitous molecular chaperones that assist a subset of essential substrate proteins to undergo productive folding to the native state. Using single particle cryo EM and image processing we have examined complexes of E. coli GroEL with the stringently GroE-dependent substrate enzyme RuBisCO from Rhodospirillum rubrum. Here we present snapshots of non-native RuBisCO - GroEL complexes. We observe two distinct substrate densities in the binary complex reminiscent of the two-domain structure of the RuBisCO subunit, so that this may represent a captured form of an early folding intermediate. The occupancy of the complex is consistent with the negative cooperativity of GroEL with respect to substrate binding, in accordance with earlier mass spectroscopy studies.
Highlights
Correct protein folding is essential for cell viability in all kingdoms of life and depends on protein quality control systems, in which molecular chaperones play a major role
The chaperonin class of molecular chaperones [2,3,4,5] was discovered as the E. coli genes GroEL and GroES of the GroE operon required for growth of bacteriophage lambda [6] and the mitochondrial form was identified as a protein folding factor [7, 8]
In this study we use single particle cryo electron microscopy to visualize folding intermediates of R. rubrum ribulose bisphosphate carboxylase oxygenase (RuBisCO) trapped within a GroEL ring at 11–12 Å resolution
Summary
Correct protein folding is essential for cell viability in all kingdoms of life and depends on protein quality control systems, in which molecular chaperones play a major role. Protein misfolding and aggregation can produce toxic species that can cause cell death in serious neurodegenerative conditions such as Alzheimer's, Parkinson's and the prion diseases, owing to a failure of chaperones to prevent the accumulation of aggregates [1]. The chaperonin class of molecular chaperones [2,3,4,5] was discovered as the E. coli genes GroEL and GroES (large and small subunit respectively) of the GroE operon required for growth of bacteriophage lambda [6] and the mitochondrial form was identified as a protein folding factor [7, 8].
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