Conserved amino acids in the N- and C-terminal domains of integral membrane transporter FhuB define sites important for intra- and intermolecular interactions.
Transport of iron(III) hydroxamates across the inner membrane of Escherichia coli is mediated by a peri-plasmic 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 cyto-plasmic 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.
Böhm
B
B
Mikrobiologie/Membranphysiologie, Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
Boschert
H
H
Köster
W
W
D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005290:Ferric Compounds / Q000378:metabolism*; D005816:Genetic Complementation Test; D006877:Hydroxamic Acids / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D033902:Periplasmic Binding Proteins; D017354:Point Mutation
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D005290:Ferric Compounds; C066629:FhuC protein, E coli; D006877:Hydroxamic Acids; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033902:Periplasmic Binding Proteins; C074579:iron (III) hydroxamate; C069968:fhuB protein, E coli