Browsing by Subject "Lipid bilayers"

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    Biophysical characterization of membrane proteins and antimicrobial peptides by solution and solid-state NMR spectroscopy.
    (2011-03) Verardi, Raffaello
    Membrane proteins and antimicrobial peptides represent two diverse and challenging classes of macromolecules to characterize at the molecular level. They are linked by the interaction with the lipid bilayer of the cell membrane. Within the lipid bilayer, membrane proteins are involved in vital biochemical processes such as ion transport, signal transduction and cell adhesion. Antimicrobial peptides are a broad class of polypeptides produced by all living organisms, representing the first line of defense against bacterial infections. They work by selectively targeting the bacterial membranes and subsequently killing the cell by a variety of mechanisms such as membrane disruption, membrane potential dissipation and enzyme inactivation. Although very important, membrane proteins and antimicrobial peptides are underrepresented in terms of available high-resolution structural information compared to water-soluble proteins and this limits the current understanding of how they work in living cells. In this thesis I summarize my contribution towards the elucidation of the high-resolution structures of the integral membrane protein phospholamban and the mechanism of action of two important antimicrobial peptides (LL37 and distinctin) by a hybrid solution and solid-state nuclear magnetic resonance spectroscopy approach. These results provide new insights and methodologies to study and understand how key membrane proteins and antimicrobial peptides elicit their function.
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    Interactions of Ethylene Oxide-Propylene Oxide Block Copolymers with Lipid Bilayers
    (2019-08) Zhang, Wenjia
    Nonionic poly(propylene oxide)-b-poly(ethylene oxide) (PPO-PEO) block copolymers, known as Pluronics or poloxamers, have been widely studied for their great potential in cell membrane stabilization and permeabilization due to their amphiphilicity and biocompatibility. A hydrophilic dominant commercial poloxamer P188 shows a reasonable stabilization effect in vivo on dystrophic muscle cell membranes. Despite recent advances made in this field, the structure-function relationships and the underlying mechanism of polymer protection are not fully understood. The goals of this dissertation are to understand the fundamental mechanism of polymer-membrane association and to further design effective polymers to improve the therapeutic approach of cell membrane stabilization for Duchenne muscular dystrophy. Herein, we developed a simple yet powerful method that enables the quantification of the relatively weak interactions between the copolymers and vesicular lipid bilayers based on distinct diffusivity of free and bound polymers, using pulsed-field-gradient NMR (PFG-NMR). This is the first quantitative study that systematically investigated polymer binding to lipid membranes in the literature to our knowledge, which provides direct evidence regarding how polymer structure and membrane composition and curvature dictate their interactions. With lab-synthesized PPO-PEO diblock analogs as complements to the commercial triblock poloxamers, we found that polymers with larger molecular weight and higher hydrophobicity result in stronger polymer-membrane association. Also, the lipid bilayer composition plays a critical role. Notably, polymer binding drops 10-fold in a universal fashion as cholesterol concentration in the bilayer increases from 0 to 30 mol.%. Switching the lipid headgroup from choline to glycerol significantly enhanced polymer binding. Additionally, polymer protection efficacy on liposomes against induced lipid peroxidation was assessed and compared with their stabilization efficacy in vitro and in vivo.