Tj. Barnard et al., Mutations in the Escherichia coli receptor FepA reveal residues involved in ligand binding and transport, MOL MICROB, 41(3), 2001, pp. 527-536
FepA is the Escherichia coli outer membrane receptor for ferric enterobacti
n, colicin D and colicin B. The transport processes through FepA are energy
-dependent, relying on the periplasmic protein TonB to interact with FepA.
Through this interaction, TonB tranduces energy derived from the cytoplasmi
c membrane across the periplasmic space to FepA. In this study, random muta
genesis strategies were used to define residues of FepA important for its f
unction. Both polymerase chain reaction (PCR)-generated random mutations in
the N-terminal 180 amino acids of FepA and spontaneous chromosomal fepA mu
tations were selected by resistance to colicin B. The PCR mutagenesis strat
egy targeted the N-terminus because it forms a plug inside the FepA barrel
that is expected to be involved in ligand binding, ligand transport, and in
teraction with TonB. We report the characterization of 15 fepA missense mut
ations that were localized to three regions of the FepA receptor. The first
region was a stretch of eight amino acids referred to as the TonB box. The
second region included extracellular loops of both the barrel and the plug
. A third region formed a cluster near the barrel wall around positions 75
and 126 of the plug. These mutations provide initial insight into the mecha
nisms of ligand binding and transport through the FepA receptor.