Novel approaches for the lipid sponge phase crystallization of the Rhodobacter sphaeroides photosynthetic reaction center

With the recent developments in the field of free electron laser based serial femtosecond crystallography, the necessity to obtain a large number of high quality crystals has emerged. In this work crystallization techniques were selected, tested and optimized for the lipid mesophase crystallization of the Rhodobacter sphaeroides membrane pigment protein complex, known as the photosynthetic reaction center RC . Novel approaches for lipid sponge phase crystallization in comparatively large volumes using Hamilton gas tight glass syringes and plastic pipetting tips are described. An analysis of RC crystal structures obtained by lipid mesophase crystallization revealed non native ligands that displaced the native electron transfer cofactors carotenoid sphero idene and a ubi quinone molecule from their binding pockets. These ligands were identified and were found to be lipids that are major mesophase components. The selection of distinct co crystallization conditions with the missing cofactors facilitated the restoration of sphero idene in its binding sit