FhuA, an XXXX outer membrane protein with a dual function of transporter and channel which mediates the transport of phage DNA.

@entity30826 @entity10588 @entity526 @entity6072
FhuA (M(r) = 78,900) is an @entity526 outer membrane protein which transports the ferric siderophore ferrichrome and is the receptor for @entity10588 , phi 80 and @entity10588 and for colicin M. FhuA was purified chromatographically in non-ionic detergent ( @entity6072 ). The circular dichroism spectrum indicates that FhuA is essentially organized in beta-strands like the majority of proteins of the outer membrane of Gram-negative bacteria. The structural parameters of FhuA were assessed from size exclusion chromatography, sedimention equilibrium and velocity experiments. FhuA is monomeric in solution and functional since binding of @entity10588 causes the release of the phage genome, a double-stranded DNA of 121,000 base pairs, into the surrounding medium. Planar lipid bilayer experiments showed that the FhuA transporter is converted into a high conductance channel upon binding of @entity10588 . FhuA was reconstituted into large unilamellar vesicles (mean diameter 125 nm). Cryo-electron microscopy and fluorescence experiments, using a DNA intercalant @entity30826 , showed that binding of @entity10588 to FhuA triggers the transfer of the phage genome into the proteoliposomes without altering their morphology. Two models can account for these observations, which apply both to in vitro and in vivo DNA transport. The simplest model supposes that the naked DNA is transported through the FhuA channel. Alternatively transfer of DNA might be mediated by pb2, the protein forming the phage straight fiber. pb2 would insert either directly in the membrane or inside the FhuA channel.
