Uptake of the butyrate receptors, GPR41 and GPR43, in lipidic bicontinuous cubic phases suitable for in meso crystallization

Abstract

The butyrate G-protein coupled receptors (GPCRs), GPR41 and GPR43, have been implicated in colorectal cancer and leptin production. To date their function has not been elucidated as low levels of protein expression and difficulties in producing diffraction quality crystals have hindered their structural determination. In meso crystallization, which uses an artificial lipid membrane matrix to facilitate crystal growth, is becoming an increasingly successful crystallization technique, particularly for GPCRs. We report herein the lipid membrane matrix structural characterization for GPR41 and GPR43 within two lipid self-assembly systems (monoolein and phytantriol) commonly used for in meso crystallization and comment on their suitability for crystallizing these GPCRs. Synchrotron small angle X-ray scattering (SAXS) studies were used to determine the initial phase and uptake of these receptors within the lipid matrix and investigate the role of cholesterol in this process. The self-assembled lipid nanostructure was retained in the presence of GPR43 for both lipids but was destabilized for GPR41 in the phytantriol lipid system. The structural changes to the lipid matrix upon protein incorporation were greater for cholesterol-doped systems, potentially indicative of increased receptor uptake.