SPECIFIC PROTEIN ATTACHMENT TO ARTIFICIAL MEMBRANES VIA COORDINATION TO LIPID-BOUND COPPER(II)

A versatile and convenient method for targeting proteins to lipid asse mblies using metal ion coordination is described. Mixed lipid bilayers and Langmuir monolayers containing a metal-chelating lipid and divale nt copper ions are shown to bind protein via surface-accessible histid ine residues. Cu2+ chelated by iminodiacetate (IDA) in the headgroup s erves as an affinity ligand to target the protein to the interface. Th e compact, uncharged Cu2+-IDA headgroup can be incorporated into lipid assemblies without disrupting the lipid packing. Surface pressure-are a isotherms of DSPC monolayers containing 5 mol % of IDA-lipid show th at Cu2+ enhances the rate and extent of myoglobin association with the interface. Myoglobin binds to small unilamellar vesicles containing 2 % Cu2+-IDA lipid (48% DSPC and 50% cholesterol) at least an order of m agnitude more tightly than to vesicles without metal or loaded with Ca 2+. The Cu2+-IDA lipid more than doubles the amount of protein targete d to the interface. Cu2+ ESR parameters g(parallel-to) and A(parallel- to), measured for liposomes with native and DEPC-modified myoglobin, s upport coordination of surface histidine side chains to Cu2+ as the bi nding interaction.