Getting Across the Membrane

Science  02 Jun 2006:
Vol. 312, Issue 5778, pp. 1273k
DOI: 10.1126/science.312.5778.1273k

Bacteria obtain essential nutrients such as vitamin B12 and iron through a family of outer membrane proteins that sequester these compounds and transport them into the periplasmic (intermembrane) space. The members of this family all adopt a barrel-like architecture and have one domain that serves as a plug. How the nutrient is moved through the barrel is unclear, although an inner membrane protein called TonB is known to participate and to supply the energy to unplug the transporter. Shultis et al. (p. 1396) and Pawelek et al. (p. 1399) have determined the structures of the complexes formed by the vitamin transporter BtuB and the iron transporter FhuA, respectively, with the C-terminal domain of TonB. In both cases, TonB induces a portion of the plug to form a β strand, which is then co-opted into a β sheet.

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