Thesis supervisor: Tibor Páli
Location of studies (in Hungarian): ELKH BRC Abbreviation of location of studies: SZBK
Description of the research topic:
Biomembranes host numerous live processes related but not limited to cellular energisation, energy conversion, transport and signalling. The main functional units of biomembranes are membrane proteins. Lipids are not only the main building constituents of biological membranes but studies in the past decades have shown that their interaction with membrane proteins is of great functional relevance too. Measurement of lipid-protein interaction requires precise control of the membrane state, in particular its fluidity. Several spectroscopic techniques measure different physical parameters related to, but not identical with membrane fluidity: Spin-label electron paramagnetic resonance (EPR) measures the rotational correlation time, orientational order and lateral diffusion of spin-label molecules embedded in the membrane. Fluorescence spectroscopy is used to measure native fluorescence of Trp residues in membrane proteins and also the lifetime and anisotropic rotation of fluorescent dyes in membranes. Fourier-transform infrared (FTIR) is a label-free technique, which can measure molecular vibrations of membrane lipids and the polypeptide backbone of proteins, yielding information on molecular conformation. Differential scanning calorimetry is the choice to study the thermodynamics and phase transitions in lipid membranes or proteins. These techniques complement each other very well in providing data on molecular structure and dynamics of (biological) membranes and membrane proteins. However, the literature lacks a detailed and consistent correspondence of the various physical parameters reported by these techniques on membrane fluidity and lipid-protein interaction, and even the use of the term "membrane fluidity" is not consistent. The present project aims at a systematic comparative study of membrane fluidity parameters using the above techniques, providing a more consistent picture of membrane dynamics:
• Model biological membranes will be measured in gel, fluid and inverted hexagonal phases of biological relevance. Our objective is also to develop new spectrum analysis and fitting algorithms in order to maximise the information on structure and dynamics from spectra measured using the most modern instruments available in the host laboratory.
• Our plan is to implement a molecular mechanics model of the bilayer and derive the spectroscopic parameters, or where possible even simulate the spectra. The comparison of the experimental and theoretical membrane dynamics parameters will ensure a consistent interpretation of membrane fluidity based on a single model.
• It will be then studied how the parameters of membrane dynamics change when integral or water-soluble proteins are present, such as subunit c or the c-ring of the vacuolar proton-ATPase or V-ATPase and lysozyme, respectively.
• So far very few studies addressed the lipid-protein interaction with these proteins, but we hypothesise that it plays in important functional role in pH regulation and antibacterial action by V-ATPase and lysozyme, respectively, since, in native V-ATPase, the c-ring (or the rotor) is in contact with membrane lipids, and lysozyme might interact with bacterial membranes.
Required language skills: English Number of students who can be accepted: 2
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