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Antiparallel Dimers of the Small Multidrug Resistance Protein EmrE Are More Stable Than Parallel Dimers
Lloris-Garcerá, Pilar Bianchi, Frans Slusky, Joanna Seppälä, Susanna Daley, Daniel O. von Heijne, Gunnar
Lloris-Garcerá, Pilar
Bianchi, Frans
Slusky, Joanna
Seppälä, Susanna
Daley, Daniel O.
von Heijne, Gunnar
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Abstract
The bacterial multidrug transporter EmrE is a dual-topology membrane protein and as such is able to insert into the membrane in two opposite orientations. The functional form of EmrE is a homodimer; however, the relative orientation of the subunits in the dimer is under debate. Using EmrE variants with fixed, opposite orientations in the membrane, we now show that, although the proteins are able to form parallel dimers, an antiparallel organization of the subunits in the dimer is preferred. Blue-native PAGE analyses of intact oligomers and disulfide cross-linking demonstrate that in membranes, the proteins form parallel dimers only if no oppositely orientated partner is present. Co-expression of oppositely orientated proteins almost exclusively yields antiparallel dimers. Finally, parallel dimers can be disrupted and converted into antiparallel dimers by heating of detergent-solubilized protein. Importantly, in vivo function is correlated clearly to the presence of antiparallel dimers. Our results suggest that an antiparallel arrangement of the subunits in the dimer is more stable than a parallel organization and likely corresponds to the functional form of the protein.
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Date
2012-06-14
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American Society for Biochemistry and Molecular Biology
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Keywords
Membrane proteins, Membrane transport, Multidrug transporters, Protein assembly, Protein-protein interactions, EmrE, Membrane protein topology, Multidrug resistance
Citation
Lloris-Garcerá, P., Bianchi, F., Slusky, J. S. G., Seppälä, S., Daley, D. O., & von Heijne, G. (2012). Antiparallel Dimers of the Small Multidrug Resistance Protein EmrE Are More Stable Than Parallel Dimers. The Journal of Biological Chemistry, 287(31), 26052–26059. http://doi.org/10.1074/jbc.M112.357590