Mechanism of Formation and Functional Properties of Lipoprotein Discs Stabilized by Amphiphilic Maleic Acid-Containing Alternating Copolymers

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Amphiphilic maleic acid-containing alternating copolymers (MACPs), in which units of maleic acid alternate with (variable) hydrocarbon units, account for a recent major methodical breakthrough in the study of membrane proteins. Several MACPs were found to solubilize membrane proteins both from artificial and natural lipid bilayers yielding discoidal MACP-encased lipid/lipoprotein particles with uniform diameter in the range from 10-30 nm. Enzymes seem to remain functional within MACP-particles; therefore, such particles make even those membrane proteins, which are unstable in the presence of detergent, accessible to techniques that require homogenous water-soluble (single) particles. It remains, however, unclear how MACPs extract membrane proteins in the absence of detergents, how the different components of the MACP-lipid/lipoprotein particle interact, and how the restricted lipid environment in these particles interferes with large scale conformational dynamics of the encased membrane protein. In a collaboration with Prof. Konstantin Shaitan, Lomonosov Moscow State University (Russia), we intend to scrutinize the properties of MACP-particles by combining experimental and theoretical approaches. Using different MACPs, we will characterize MACP-lipid/lipoprotein particles by size exclusion chromatography, dynamic light scattering, atomic-force microscopy, transmission electron microscopy, and EPR spectroscopy. As a functional detector the complex of the light sensitive archaeal sensory rhodopsin and its cognate transducer protein will be inserted into MACP-particles. Its protein dynamics will be followed on different time scales using time resolved optical and EPR spectroscopy to understand, how the nature of MACPs affects the light-induced signal transduction within the complex. Concurrently, our collaboration partner will model MACP-particles and analyze them by molecular dynamic simulations to assess how electrostatic, hydrophobic and stacking interactions stabilize the particles. The goals of the project are to draw a physico-chemical picture of formation and stabilization of MACP-encased lipid/lipoprotein nanoparticles and to develop optimized protocols of protein extraction by MACPs yielding native-like environments within MACP-lipid/lipoprotein particles.