8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P7.118Thu 811:10-14:00Diffusion of lysozyme molecules confined in lipidmonoolein cubic phasesShinpei Tanaka 11 Hiroshima University, 1-7-1 Kagamiyama, 739-8521, Higashi-Hiroshima, JapanLipid cubic phases consist of interconnected water channels surrounded by lipid membranes. Thewidth of the channel can be as small as several nanometers which roughly corresponds to the sizeof a protein molecule. It has been shown that protein lysozyme crystallization is enhanced whenconfined in the water channels of the monoolein cubic phases [1], due to the entropic frustrationinduced by the confinement. The confinement of protein molecules in the water channels, on theother hand, affects the structure of the cubic phase. When lysozyme concentration was increased,the Pn3m structure, most stable structure if protein is absent, changes to the Im3m structure [2].This is because the Im3m structure has wider channels than the Pn3m structure. In this study,we focus on the diffusion of lysozyme molecules confined in the water channels. The diffusioncoefficient of lysozyme, D, was measured by the fluorescence correlation spectroscopy using fluorescentlylabeled lysozyme molecules. The D of confined lysozyme was about 20 times smallerthe one in a bulk solution when the lysozyme concentration in the channel was in the dilute limit.With the increase of the concentration, D decreased about 10 times. We conducted a Browniandynamics simulation using model protein particles confined in model cubic structures to elucidatethe dependence of D on the concentration. It turned out that D increased with the increase of theconcentration in the channels if the channel structure was fixed with the Pn3m. On the other hand,Im3m structure prevented any particle diffusion in our model. The results suggested that lysozymemolecules moved in a microscopically deformed cubic phase structures, which was the mixture ofthe Pn3m structure and Im3m structure.[1] S. Tanaka, S. U. Egelhaaf, and W. C. K. Poon, Phys. Rev. Lett. 92 (2004) 128102.[2] S. Tanaka, S. Maki, and M. Ataka, Phys. Rev. E. 73 (2006) 061510.118