ATP-LIPIDS - PROTEIN ANCHOR AND ENERGY-SOURCE IN 2 DIMENSIONS

The ubiquitous function of ATP as energy equivalent in nature has resu lted in a common folding pattern of ATP-binding proteins. Their bindin g pocket tolerates modifications of the adenine ring to some extend, w hereas those of the triphosphate group strongly affect the binding aff inity. In consequence, immobilized C8- and N-6- modified ATP analogues are frequently used for affinity purification of ATPases or kinases. To combine this unique recognition principle with the fascinating prop erties of self-assembly, we have synthesized a novel class of hydrolyz able and nonhydrolyzable ATP-lipids where the nucleotides are covalent ly attached via C8- or N-6-position of the adenine ring to a synthetic lipid. These ATP-lipids were characterized by various enzyme assays i n micellar solution, resulting in ATPase and competition activities th at are comparable to their free counterparts. The specific docking of actin as a model of an ATP-binding protein to ATP-lipid monolayers was followed by film balance technique and epifluorescence microscopy. Ba sed on this specific interaction, actin-supported membranes were gener ated to study shape transitions of vesicular systems. Due to the coupl ing of actin to ATP-lipid bilayers drastic changes in the viscoelastic properties and shape transitions were observed by phase contrast micr oscopy. These results underline the properties of these novel ATP-lipi ds as protein anchor or energy source in two dimensions. They can be a pplied either to form phantom cells, actin-supported membranes or to o rient and crystallize ATP-binding proteins at lipid interfaces.