Structural Basis of Gating by the Outer Membrane Transporter FecA
Andrew D. Ferguson,1
Ranjan Chakraborty,23
Barbara S. Smith,1
Lothar Esser,14
Dick van der Helm,25
Johann Deisenhofer1*
Siderophore-mediated acquisition systems facilitate iron uptake. We
present the crystallographic structure of the integral outer membrane
receptor FecA from Escherichia coli with and without ferric
citrate at 2.5 and 2.0 angstrom resolution. FecA is composed of three
distinct domains: the barrel, plug, and NH2-terminal extension. Binding of ferric citrate triggers a conformational change
of the extracellular loops that close the external pocket of FecA.
Ligand-induced allosteric transitions are propagated through the outer
membrane by the plug domain, signaling the occupancy of the receptor in
the periplasm. These data establish the structural basis of gating for
receptors dependent on the cytoplasmic membrane protein TonB. By
compiling available data for this family of receptors, we propose a
mechanism for the energy-dependent transport of siderophores.
1 Howard Hughes Medical Institute and
Department of Biochemistry, University of Texas Southwestern Medical
Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
2 Department of Chemistry and Biochemistry,
University of Oklahoma, 620 Parrington Oval, Norman, OK 73019, USA.
3 Department of Health Sciences, College of Public
and Allied Health, East Tennessee State University, Post Office Box
70673, Johnson City, TN 37614, USA.
4 Laboratory of
Cell Biology, National Cancer Institute, National Institutes of Health,
37 Convent Drive, Bethesda, MD 20892, USA.
5 Department of Biochemistry and Microbiology,
University of Victoria, Post Office Box 3055, Victoria, British
Columbia V8W 3P6, Canada.
*
To whom correspondence should be addressed. E-mail:
johann.deisenhofer{at}utsouthwestern.edu
