Crucial role of the lipid part of lipopolysaccharide for conformational change of minor spike H protein of bacteriophage ϕX174

The contribution of the lipid part of lipopolysaccharide (LPS) to recognition by minor spike H protein of bacteriophage ϕX174 was investigated by comparing the interactions of H protein with LPS and its deacylated derivatives. The fluorescence and circular dichroism (CD) spectra of H protein increased upon binding to intact LPS and a partially deacylated derivative. In contrast, completely deacylated derivatives showed lower affinities and almost no fluorescence or CD changes of H protein. These results demonstrate that the lipid part of LPS is responsible for the conformational change of minor spike H protein, which would function as a trigger for phage DNA ejection for infection of the host cell.