Theoretical and experimental study of protein-lipid interactions
Theoretische und experimentelle Untersuchung von Protein-Lipid Wechselwirkungen
Vesselka Petrova Ivanova
Doctoral thesis
Date of Examination:
2000-11-01
Date of issue:
2000-12-13
Advisor:
Heimburg, Thomas PD Dr.
Referee:
Kree, Reiner Prof. Dr.
Referee:
Heimburg, Thomas PD Dr.
Persistent Address: http://hdl.handle.net/11858/00-1735-0000-0006-B5A6-8
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Dissertation
Abstract
English
The thermotropic behavior of a lipid membrane incorporating small integral proteins is investigated. The theory is based on the two-state Ising model of which the distribution of states is explored by Monte Carlo simulations. The complete information of the degeneracy of states of a single-component lipid monolayer system is sampled in one broad histogram. The histogram method for Monte Carlo data analysis is first applied to generate fits of experimentally measured heat capacity profiles of three different vesicle preparations. In the general case of a lipid membrane incorporating small peptides, two component Monte Carlo simulations are performed. The peptide aggregation within the membrane plane results from the different solubility in the gel and the fluid phase. The information about the density of states in this case is sampled in a broad four-dimensional histogram. From the comparison of the theoretical calculations to the experimentally measured heat capacity profiles, the aggregation of the peptide gramicidin A in the gel and the fluid phase of DPPC and DMPC bilayer is predicted. These predictions are tested by means of the atomic force microscopy technique and a good agreement is found. The information sampled in the monolayer histogram is used to resolve lipid relaxation properties near the chain-melting transition. The relaxation times resolved characterize the decay of the enthalpy fluctuations. The proportionality relation between the relaxation time and the heat capacity, estimated theoretically agrees well with the results by pressure-calorimetry experiments.
Keywords: lipid membranes; peptides; Monte Carlo; histogram method; calorimetry; AFM; lipid kinetics
