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Macromolecular crowding extended to a heptameric system: the co-chaperonin protein 10
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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2011 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 50, no 14, 3034-3044 p.Article in journal (Refereed) Published
Abstract [en]

Experiments on monomeric proteins have shown that macromolecular crowding can stabilize toward heat perturbation and also modulate native-state structure. To assess the effects of macromolecular crowding on unfolding of an oligomeric protein, we here tested the effects of the synthetic crowding agent Ficoll 70 on human cpn10 (GroES in E. coli), a heptameric protein consisting of seven identical β-barrel subunits assembling into a ring. Using far-UV circular dichroism (CD), tyrosine fluorescence, nuclear magnetic resonance (NMR), and cross-linking experiments, we investigated thermal and chemical stability, as well as the heptamer-monomer dissociation constant, without and with crowding agent. We find that crowding shifts the heptamer-monomer equilibrium constant in the direction of the heptamer. The cpn10 heptamer is both thermally and thermodynamically stabilized in 300 mg/mL Ficoll 70 as compared to regular buffer conditions. Kinetic unfolding experiments show that the increased stability in crowded conditions, in part, is explained by slower unfolding rates. A thermodynamic cycle reveals that in presence of 300 mg/mL Ficoll the thermodynamic stability of each cpn10 monomer increases by over 30%, whereas the interfaces are stabilized by less than 10%. We also introduce a new approach to analyze the spectroscopic data that makes use of multiple wavelengths: this provides robust error estimates of thermodynamic parameters.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2011. Vol. 50, no 14, 3034-3044 p.
National Category
Chemical Sciences
URN: urn:nbn:se:umu:diva-43730DOI: 10.1021/bi2002086PubMedID: 21375247OAI: diva2:415659
Available from: 2011-05-09 Created: 2011-05-09 Last updated: 2014-01-20Bibliographically approved
In thesis
1. Folding and interaction studies of subunits in protein complexes
Open this publication in new window or tab >>Folding and interaction studies of subunits in protein complexes
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Proteins function as worker molecules in the cell and their natural environment is crowded. How they fold in a cell-like environment and how they recognize their interacting partners in such conditions, are questions that underlie the work of this thesis.

Two distinct subjects were investigated using a combination of biochemical- and biophysical methods. First, the unfolding/dissociation of a heptameric protein (cpn10) in the presence of the crowding agent Ficoll 70. Ficoll 70 was used to mimic the crowded environment in the cell and it has been used previously to study macromolecular crowding effects, or excluded volume effects, in protein folding studies. Second, the conformational changes upon interaction between the Mediator subunit Med25 and the transcription factor Dreb2a from Arabidopsis thaliana. Mediator is a transcriptional co-regulator complex which is conserved from yeast to humans. The molecular mechanisms of its action are however not entirely understood. It has been proposed that the Mediator complex conveys regulatory signals from promoter-bound transcription factors (activators/repressors) to the RNA polymerase II machinery through conformational rearrangements.

The results from the folding study showed that cpn10 was stabilized in the presence of Ficoll 70 during thermal- and chemical induced unfolding (GuHCl). The thermal transition midpoint increased by 4°C, and the chemical midpoint by 0.5 M GuHCl as compared to buffer conditions. Also the heptamer-monomer dissociation was affected in the presence of Ficoll 70, the transition midpoint was lower in Ficoll 70 (3.1 μM) compared to in buffer (8.1 μM) thus indicating tighter binding in crowded conditions. The coupled unfolding/dissociation free energy for the heptamer increased by about 36 kJ/mol in Ficoll. Altogether, the results revealed that the stability effect on cpn10 due to macromolecular crowding was larger in the individual monomers (33%) than at the monomer-monomer interfaces (8%).

The results from the interaction study indicated conformational changes upon interaction between the A. thaliana Med25 ACtivator Interaction Domain (ACID) and Dreb2a. Structural changes were probed to originate from unstructured Dreb2a and not from the Med25-ACID. Human Med25-ACID was also found to interact with the plant-specific Dreb2a, even though the ACIDs from human and A. thaliana share low sequence homology. Moreover, the human Med25-interacting transcription factor VP16 was found to interact with A. thaliana Med25. Finally, NMR, ITC and pull-down experiments showed that the unrelated transcription factors Dreb2a and

VP16 interact with overlapping regions in the ACIDs of A. thaliana and human Med25.

The results presented in this thesis contribute to previous reports in two different aspects. Firstly, they lend support to the findings that the intracellular environment affects the biophysical properties of proteins. It will therefore be important to continue comparing results between in vitro and cell-like conditions to measure the magnitude of such effects and to improve the understanding of protein folding and thereby misfolding of proteins in cells. Better knowledge of protein misfolding mechanisms is critical since they are associated to several neurodegenerative diseases such as Alzheimer’s and Parkinson's. Secondly, our results substantiate the notion that transcription factors are able to bind multiple targets and that they gain structure upon binding. They also show that subunits of the conserved Mediator complex, despite low sequence homologies, retain a conserved structure and function when comparing evolutionary diverged species.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2014. 57 p.
Macromolecular crowding, cpn10, Mediator, Med25, Dreb2a, VP16, conformational changes, NMR, ITC.
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry; Molecular Biology
urn:nbn:se:umu:diva-84726 (URN)978-91-7459-795-0 (ISBN)
Public defence
2014-02-14, KBC-huset, KB3A9, Umeå universitet, Umeå, 09:00 (English)
Available from: 2014-01-24 Created: 2014-01-17 Last updated: 2014-07-11Bibliographically approved

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Aguilar, XimenaWeise, ChristophSparrman, TobiasWolf-Watz, MagnusWittung-Stafshede, Pernilla
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