Probing the Binding Modes of a Multidomain Protein to Lipid-based Nanoparticles by Relaxation-based NMR.

The interactions of two model multidomain proteins-covalently linked diubiquitins, Ub2-with lipid-based nanoparticles have been quantitatively probed by the measurements of NMR lifetime line broadening, ΔR2. By combined analysis of ΔR2 profiles arising from interactions with liposomes of varying sizes, an approach recently developed for the characterization of interactions of monoubiquitin with liposomes, we determine how the parameters of exchange (liposome binding) and dynamics of each individual domain of Ub2 on the surface of liposomes change when the domains are covalently attached to one another by a flexible linker. Two different covalent linkages were used: K63-linked and K48-linked Ub2. The possibility of three distinct modes of binding of Ub2 to liposomes requires the introduction of simple but important modifications to the strategy of analysis originally developed for monoubiquitin.