CryoEM reveals the stochastic nature of individual ATP binding events in a group II chaperonin.
Nat Commun 2021;
12:4754. [PMID:
34362932 PMCID:
PMC8346469 DOI:
10.1038/s41467-021-25099-0]
[Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Accepted: 07/21/2021] [Indexed: 12/05/2022] Open
Abstract
Chaperonins are homo- or hetero-oligomeric complexes that use ATP binding and hydrolysis to facilitate protein folding. ATP hydrolysis exhibits both positive and negative cooperativity. The mechanism by which chaperonins coordinate ATP utilization in their multiple subunits remains unclear. Here we use cryoEM to study ATP binding in the homo-oligomeric archaeal chaperonin from Methanococcus maripaludis (MmCpn), consisting of two stacked rings composed of eight identical subunits each. Using a series of image classification steps, we obtained different structural snapshots of individual chaperonins undergoing the nucleotide binding process. We identified nucleotide-bound and free states of individual subunits in each chaperonin, allowing us to determine the ATP occupancy state of each MmCpn particle. We observe distinctive tertiary and quaternary structures reflecting variations in nucleotide occupancy and subunit conformations in each chaperonin complex. Detailed analysis of the nucleotide distribution in each MmCpn complex indicates that individual ATP binding events occur in a statistically random manner for MmCpn, both within and across the rings. Our findings illustrate the power of cryoEM to characterize a biochemical property of multi-subunit ligand binding cooperativity at the individual particle level.
The mechanism by which chaperonins coordinate ATP utilization in their multiple subunits remains unclear. Here, the authors employ an approach that uses cryo-EM single particle analysis to track the number and distribution of nucleotides bound to each subunit in the homo-oligomeric MmCpn archaeal chaperonin complex and observe that ATP binds in a statistically random manner to MmCpn both within a ring and across the rings, which shows that there is no cooperativity in ATP binding to archaeal group II chaperonins under the conditions used in this study.
Collapse