1. [Untitled]
- Author
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Barbara S. Smith, Lalitha Venkatramani, Dick Van der Helm, Johann Deisenhofer, Di Xia, Ranjan Chakraborty, Maya Palnitkar, Lothar Esser, and Susan K. Buchanan
- Subjects
Inner membrane complex ,Siderophore transport ,biology ,Chemistry ,Membrane transport protein ,Antiporter ,Membrane transport ,Biochemistry ,Crystallography ,Structural Biology ,Genetics ,FepA ,biology.protein ,Outer membrane efflux proteins ,Bacterial outer membrane - Abstract
Integral outer membrane receptors for iron chelates and vitamin B12 carry out specific ligand transport against a concentration gradient. Energy for active transport is obtained from the proton-motive force of the inner membrane through physical interaction with TonB-ExbB-ExbD, an inner membrane complex. Here we report the crystal structure of an active transport, outer membrane receptor at 2.4 A resolution. Two distinct functional domains are revealed: (i) a 22-stranded beta-barrel that spans the outer membrane and contains large extracellular loops which appear to function in ligand binding; and (ii) a globular N-terminal domain that folds into the barrel pore, inhibiting access to the periplasm and contributing two additional loops for potential ligand binding. These loops could provide a signaling pathway between the processes of ligand recognition and TonB-mediated transport. The blockage of the pore suggests that the N-terminal domain must undergo a conformational rearrangement to allow ligand transport into the periplasm.
- Published
- 1999