Interdomain interactions within the gene 3 protein of filamentous phage

Infection of Escherichia coli by filamentous phage fd is mediated by the phage gene 3 protein (g3p), Th g3p consists of three domains (g3p-D1, D2 and D3) linked by flexible glycine-rich linkers, AII three domains are indispensable for phage infectivity; the g3p-D1 domain hinds to the TolA receptor presumably at the inner face of the outer membrane, the g3p-D2 domain to the F-pilus and the g3p-D3 domain anchors g3p to the phage coat, The N-terminal domains g3p-D1 and D2 interact with each other: this interaction is abrogated by binding of g3p-D2 to the F-pilus leading to the release of g3p-D1 to bind to TolA. Here, using phages with deletions in g3p, we have discovered a specific interaction between the two N-terminal domains slid g3p-B3, the C-terminal domain of g3p, We propose that these interdomain interactions within g3p lead to a compact and stable organisation when displayed on the phage tip, but that during infection, this compact state must be unraveled, (C) 1999 Federation of European Biochemical Societies.