MODELING LIGAND-GATED RECEPTOR ACTIVITY - FHUA-MEDIATED FERRICHROME EFFLUX FROM LIPID VESICLES TRIGGERED BY PHAGE T5

An in vitro assay of iron-ferrichrome translocation across the FhuA pr otein of outer membranes from Escherichia coli has been devised. Upon reconstitution into large lipid vesicles, bacteriophage T5 binds to th is polyvalent receptor, triggering a conformational change that result ed in channel opening. This facilitates the translocation of an iron(I II)-siderophore, without the complexities involved in the in vivo proc ess. Efflux of Fe-55(III)-ferrichrome across FhuA channels was determi ned quantitatively by monitoring the release of trapped radioactivity. The assay is rapid, reliable, and specific, because other bacteriopha ges, such as Phi 80, fail to trigger channel opening of the FhuA recep tor.