Light-induced coupling of aqueous-soluble proteins to liposomes formed from carbene-generating phospholipids

A novel bilayer-forming phospholipid analogue with a photoactivatable carbene-generating head group was synthesized and characterized with respect to molecular structure and light-induced reactivity. N'-(1,2-Dimyristoyl-sn-glycero-3-phosphoethyl)-N-[m-[3- (trifluoromethyl)diazirin-3-yl]phenyl]thiourea (PED) was prepared by thiocarbamoylation of synthetic dimyristoylphosphatidylethanolamine with 3-(trifluoromethyl)-3-(m-isothiocyanophenyl)diazirine. PED formed liposomes in aqueous media. Gel to liquid-crystalline transitions occurred at 10.5 degrees C. Neither PED- nor PED/dimyristoylphosphatidylcholine mixed liposomes underwent major structural changes when photoactivated. Liposome sizes, determined by electron microscopy, were not altered upon light exposure. PED combines the advantages of facile synthesis and timed carbene reactivity by photoactivation at wavelengths greater than or equal to 320 nm. Conditions used for PED photoactivation did not inactivate catalytically active or complex-forming proteins. Light-induced binding of aqueous-soluble proteins to PED containing liposomes was attained through photoactivation in the presence of myoglobin, streptavidin, or trypsin. The proteins mentioned were utilized to characterize carbene-initiated ligand coupling. Procedures described establish a new and versatile method for the formation of proteoliposomes.