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Science  23 Aug 2002:
Vol. 297, Issue 5585, pp. 1241a
DOI: 10.1126/science.297.5585.1241a

A recurring structural motif in membrane proteins is a bundle of α helices whose axis is oriented perpendicularly to the plane of the membrane. For TolC, this bundle spans the 10-nm periplasmic gap between the inner and outer membranes of Gram-negative bacteria. Andersen et al. have used the crystal structure of TolC in the closed state to design mutations in interhelical contacts that serve to reduce the overall twist of the individual helices, thus unwinding the bundle slightly and creating a central passageway about 1.5 nm in diameter. They propose that reversible disruption of these contacts provides a mechanism for regulated export of proteins and antibiotics (in self-defense as well as in combat against other bacteria). Detailed studies of the transmembrane helical bundle of the mechanosensitive channel MscL by Perozo et al. and Betanzos et al. lend support to the generality of helical twisting as a means of controlling permeability. — GJC

Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.162039399 (2002); Nature Struct. Biol. 10.1038/nsb827; 10.1038/nsb828 (2002).

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