Berlin 2012 – scientific programme

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BP: Fachverband Biologische Physik

BP 26: Posters: Membranes and Vesicles

BP 26.23: Poster

Thursday, March 29, 2012, 17:30–19:30, Poster A

Partitioning of cytochrome c in multicomponent lipid membranes with domains — •Salome Pataraia — Max-Planck-Institute of Colloids and Interfaces Theory & Bio-Systems Potsdam

We characterized the binding of cytochrome c (cyt c), a mitochondrial inner membrane protein, to multicomponent lipid membranes and resolved the role of the bilayer surface charge and lipid composition. As a model system, giant unilamellar vesicles (GUVs) were used. To mimic the membrane composition of the inner mitochondrial membrane we employed lipid mixtures of the charged dioleoyphosphatidylcholine (DOPG), sphingomyelin (SM) and cholesterol. We first characterized the phase behavior of this mixture from confocal microscopy observations on fluorescently labeled GUVs. We localised the region of coexistence of liquid ordered (Lo) and liquid disordered (Ld) phases, mimicking raft-like domains and their environment in cell membranes. We then investigated the change in the phase state of these membranes induced by cyt c at physiological concentrations. Our studies revealed that in the presence of cyt c, the area of the Lo-Ld coexistence region increases on the expense of the single-phase Ld region. By means of fluorescent intensity studies, we also studied the preferential partitioning of cyt c between the Ld and Lo phases. Our results indicate that cyt c strongly prefers the DOPG-rich Ld domains. The specific affinity of the protein to each of the fluid phases are thermodynamically quantified with isothermal titration calorimetry on large unilamellar vesicles with compositions characteristic of either the Lo or the Ld phase.