Iron-hydroxamate transport into Escherichia coli K12: localization of FhuD in the periplasm and of FhuB in the cytoplasmic membrane |
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Authors: | Wolfgang K?ster and Volkmar Braun |
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Institution: | (1) Mikrobiologie II, Universit?t Tübingen, D-7400 Tübingen, Federal Republic of Germany |
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Abstract: | Summary ThefhuB, fhuC andfhuD genes encode proteins which catalyze transport of iron(III)-hydroxamate compounds from the periplasm into the cytoplasm ofEscherichia coli. ThefhuB, C, D genes were cloned downstream of a strong phage T7 promoter and transcribed by T7 RNA polymerase. The overexpressed FhuD protein
appeared in two forms of 31 and 28 kDa and was released upon conversion of vegetative cells into spheroplasts, suggesting
synthesis of FhuD as a precursor and export into the periplasm. The very hydrophobic FhuB protein was found in the cytoplasmic
membrane. These properties, together with the previously found homologies in the FhuC protein to ATP-binding proteins, display
the characteristics of a periplasmic binding protein dependent transport system across the cytoplasmic membrane. The molecular
weight of FhuB and the sequence offhuC, as previously published by us, was confirmed. FhuB exhibited double the size of most hydrophobic proteins of such systems
and showed homology between the amino- and carboxy-terminal halves of the protein, indicating duplication of an original gene
and subsequent fusion of the two DNA fragments. |
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Keywords: | Escherichia coli Iron-hydroxamate transport fhuB C D genes |
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