SEQUENCE OF THE FHUE OUTER-MEMBRANE RECEPTOR GENE OF ESCHERICHIA-COLI K12 AND PROPERTIES OF MUTANTS

The fhuE gene of Escherichia coli codes for an outer‐membrane receptor protein required for the uptake of iron(III) via coprogen, ferrioxamine B and rhodotorulic acid. The amino acid sequence, deduced from the nucleotide sequence, consisted of 729 residues. The mature form, composed of 693 residues, has a calculated molecular weight of 77453, which agrees with the molecular weight of 76000 determined by poly‐acrylamide gel electrophoresis. The FhuE protein contains four regions of homology with other TonB‐dependent receptors. A valine to proline exchange in the ‘TonB box’ absolished transport activity. Phenotypic revertants with substitutions of arginine, glutamine, or leucine at the valine position exhibited Increasing iron‐coprogen transport rates. Point mutations resulting in the replacement of glycine (127) in the second homology region with either alanine, aspartate, valine, asparagine or histidine exhibited decreased transport rates (listed in descending order). A truncated FhuE protein lacking 24 amino acids at the C‐terminal end was exported to the periplasm but failed to be inserted into the outer membrane. Copyright © 1990, Wiley Blackwell. All rights reserved