Reconstituting Transport Proteins

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Science  02 Mar 2007:
Vol. 315, Issue 5816, pp. 1189k
DOI: 10.1126/science.315.5816.1189k

The few available crystal structures of membrane-transport proteins generally reveal internal symmetry, either about an axis perpendicular to the membrane or, somewhat more surprisingly, about an axis within the plane of the membrane. Transporters in the first class contain two structurally similar domains that exhibit the same membrane topology, which yields an even (2n) number of membrane-spanning helices, whereas those in the second class have oppositely oriented domains and an odd (2n+1) number of helices. By making stepwise modifications to the bacterial drug efflux pump EmrE, Rapp et al. (p. 1282, published online 25 January; see the Perspective by Poolman et al.) show how a functional dimer might evolve from a monomer (containing n helices) that can have either membrane topology.

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