Conserved amino acids in the N- and C-terminal domains of integral membrane transporter FhuB define sites important for intra- and intermolecular interactions |
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Authors: | Brigitte Böhm Hartmut Boschert Wolfgang Köster |
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Institution: | Mikrobiologie/Membranphysiologie, Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. |
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Abstract: | 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 (FhuBN] and FhuBC]) 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 FhuBN]–FhuBC] 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 FhuBN] and FhuBC] are primarily involved in the interaction with another component of the transport system, probably FhuC. |
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