FLUORESCENCE SIGNALING OF LIGAND-BINDING AND ASSEMBLY IN METAL-CHELATING LIPID-MEMBRANES

Background: Chemical information is sometimes transmitted across cell membranes by ligand-induced assembly of receptors, We have previously designed a series of lipids with metal-chelating headgroups that can s erve as general receptors for proteins containing accessible histidine s. Such lipids can also be derivatized with pyrene, a fluorescent prob e that has a different emission maximum when it is aggregated (excimer fluorescence) from that seen for the monomer, We set out to examine w hether lipids of this kind would produce a signal in response to ligan d binding. Results: A model ligand, poly-L-histidine (poly(His)), boun d specifically to pyrene-labeled Cu(II)-iminodiacetate lipid (Cu-PSIDA ) within a membrane matrix. Binding of poly(His) induces the redistrib ution of Cu-PSIDA, so that it forms pyrene-rich domains that are detec table by the increased ratio of excimer to monomer fluorescence. Using rhodamine-labeled poly(His), we have shown that the receptor lipid do mains correspond to poly(His)-rich domains below the lipid interlace. Conclusions: The Cu-PSIDA receptor signals binding of the macromolecul ar ligand through its excimer fluorescence and allows the resulting do mains formed by ligand assembly to be imaged, Fluorescent Cu-PSIDA can thus serve as an optical reporter of ligand-induced lipid reorganizat ion.