Conserved amino acids in the N- and C-terminal domains of integral membrane transporter FhuB define sites important for intra- and intermolecular interactions

Authors

  • Brigitte Böhm,

    1. Mikrobiologie/Membranphysiologie, Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
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  • Hartmut Boschert,

    1. Mikrobiologie/Membranphysiologie, Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
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  • Wolfgang Köster

    Corresponding author
    1. Mikrobiologie/Membranphysiologie, Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
    • *For correspondence. Tel. (7071) 29 4632; Fax (7071) 29 4634.

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Summary

Transport of iron(III) hydroxamates across the inner membrane of Escherichia coli is mediated by a periplasmic binding protein-dependent transport (PBT) mechanism. FhuB, the integral membrane component of the system, is composed of covalently linked halves (FhuB[N] and FhuB[C]) which still function when present as two distinct polypeptide chains. Our analysis of two uptake-deficient FhuB derivatives provides evidence for a mechanistically novel type of functional complementation:‘domain displacement’ in the cytoplasmic membrane. Amino acid residues 60 and 426 in the FhuB polypeptide chain may define key positions that are important for FhuB[N]–FhuB[C] interaction. Furthermore, FhuB derivatives, altered in either one of their conserved regions - typical of PBT related integral membrane proteins - displayed a dominant negative effect on ferric hydroxamate transport. The experimental data suggest that the two functionally equivalent conserved regions in FhuB[N] and FhuB[C] are primarily involved in the interaction with another component of the transport system, probably FhuC.

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