Molecular dynamics (MD) simulations of uncoupling proteins (UCP), a class of transmembrane proteins relevant for proton transport across inner mitochondrial membranes, represent a complicated task due to the lack of available structural data. In this work, we use a combination of homology modelling and subsequent microsecond molecular dynamics simulations of UCP2 in the DOPC phospholipid bilayer, starting from the structure of the mitochondrial ATP/ADP carrier (ANT) as a template. We show that this protocol leads to a structure that is impermeable to water, in contrast to MD simulations of UCP2 structures based on the experimental NMR structure. We also show that ATP binding in the UCP2 cavity is tight in the homology modelled structure of UCP2 in agreement with experimental observations. Finally, we corroborate our results with conductance measurements in model membranes, which further suggest that the UCP2 structure modeled from ANT protein possesses additional key functional elements, such as a fatty acid-binding site at the R60 region of the protein, directly related to the proton transport mechanism across inner mitochondrial membranes.

Department of Biomedical Sciences Institute of Physiology Pathophysiology and Biophysics University of Veterinary Medicine 1210 Vienna Austria

Division of Organic Chemistry and Biochemistry Ruđer Bošković Institute Bijenička 54 10000 Zagreb Croatia

Institute of Organic Chemistry and Biochemistry Czech Academy of Sciences Flemingovo nám 2 16610 Prague Czech Republic

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Exploring the proton transport mechanism of the mitochondrial ADP/ATP carrier: FA-cycling hypothesis and beyond

FA Sliding as the Mechanism for the ANT1-Mediated Fatty Acid Anion Transport in Lipid Bilayers