Functionalization of Cobalt Porphyrin-Phospholipid Bilayers with His-tagged Ligands and Antigens

Methods to attach polypeptides to lipid bilayers are often indirect, ineffective and can represent a substantial bottleneck in the formation of functionalized lipid-based materials. Although the polyhistidine tag (his-tag) has been transformative in its simplicity and efficacy in binding to immobilized metals, the successful application of this approach has been challenging in physiological settings. Here we show that lipid bilayers containing porphyin-phospholipid that is chelated with cobalt, but not other metals, can effectively capture his-tagged proteins and peptides. The binding follows a Co(II) to Co(III) transition and occurs within the sheltered hydrophobic bilayer, resulting in essentially irreversible attachment in serum or in million-fold excess of competing imidazole. Using this approach we anchored homing peptides into the bilayer of preformed and cargo-loaded liposomes to enable tumour-targeting without disrupting the bilayer integrity. As a further demonstration, a synthetic HIV-derived protein fragment was bound to immunogenic liposomes for potent antibody generation for an otherwise non-antigenic peptide.