Functional Oligomeric Forms of Uncoupling Protein 2: Strong Evidence for Asymmetry in Protein and Lipid Bilayer Systems
- 29 December 2020
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry B
- Vol. 125 (1), 169-183
- https://doi.org/10.1021/acs.jpcb.0c09422
Abstract
Stoichiometry of uncoupling proteins (UCPs) and their coexistence as functional monomeric and associated forms in lipid membranes remain intriguing open questions. In this study, tertiary and quaternary structures of UCP2 were analyzed experimentally and through molecular dynamics (MD) simulations. UCP2 was overexpressed in the inner membrane of Escherichia coli, then purified and reconstituted in lipid vesicles. Structure and proton transport function of UCP2 were characterized by circular dichroism (CD) spectroscopy and fluorescence methods. Findings suggest a tetrameric functional form for UCP2. MD simulations conclude that tetrameric UCP2 is a dimer of dimers, is more stable than its monomeric and dimeric forms, is asymmetrical and induces asymmetry in the membrane’s lipid structure, and a biphasic on–off switch between the dimeric units is its possible mode of transport. MD simulations also show that the water density inside the UCP2 monomer is asymmetric, with the cytoplasmic side having a higher water density and a wider radius. In contrast, the structurally comparable adenosine 5′-diphosphate (ADP)/adenosine 5′-triphosphate (ATP) carrier (AAC1) did not form tetramers, implying that tetramerization cannot be generalized to all mitochondrial carriers.Keywords
Funding Information
- Canada Foundation for Innovation (05437, 05900, 11292, 6786)
- Canada Research Chairs
- Natural Sciences and Engineering Research Council of Canada
- Ontario Trillium Foundation
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