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ATP-LipidsProtein Anchor and Energy Source in Two Dimensions

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posted on 19.06.1996, 00:00 by Lutz Schmitt, Robert Tampé
The ubiquitous function of ATP as energy equivalent in nature has resulted in a common folding pattern of ATP-binding proteins. Their binding pocket tolerates modifications of the adenine ring to some extend, whereas those of the triphosphate group strongly affect the binding affinity. In consequence, immobilized C8- and N6-modified ATP analogues are frequently used for affinity purification of ATPases or kinases. To combine this unique recognition principle with the fascinating properties of self-assembly, we have synthesized a novel class of hydrolyzable and nonhydrolyzable ATP-lipids where the nucleotides are covalently attached via C8- or N6-position of the adenine ring to a synthetic lipid. These ATP-lipids were characterized by various enzyme assays in micellar solution, resulting in ATPase and competition activities that 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. Based on this specific interaction, actin-supported membranes were generated to study shape transitions of vesicular systems. Due to the coupling of actin to ATP-lipid bilayers drastic changes in the viscoelastic properties and shape transitions were observed by phase contrast microscopy. These results underline the properties of these novel ATP-lipids as protein anchor or energy source in two dimensions. They can be applied either to form phantom cells, actin-supported membranes or to orient and crystallize ATP-binding proteins at lipid interfaces.