CONVERSION OF THE COPROGEN TRANSPORT PROTEIN FHUE AND THE FERRIOXAMINE-B TRANSPORT PROTEIN FOXA INTO FERRICHROME TRANSPORT PROTEINS

The FhuA protein of Escherichia coli K-12 transports ferrichrome and t he structurally related antibiotic albomycin across the outer membrane and serves as a receptor for the phages T1, T5, and phi 80 and for co licin M. In this paper, we show that chimeric proteins consisting of t he central part of FhuA and the N- and C-terminal parts of FhuE (copro gen receptor) or the N-and/or C-terminal parts of FoxA (ferrioxamine B receptor), function as ferrichrome transport proteins. Although the h ybrid proteins contained the previously identified gating loop of FhuA , which is the principal binding site of the phages T5, T1, and phi 80 , only the hybrid protein consisting of the N-terminal third of FoxA a nd the C-terminal two thirds of FhuA conferred weak phage sensitivity to cells. Apparently, the gating loop is essential, but not sufficient for wild-type levels of ferrichrome transport and for phage sensitivi ty. The properties of FhuA-FoxA hybrids suggest different regions of t he two receptors for ferric siderophore uptake. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V .