CHOLESTEROL CRYSTAL FORMATION IN REAL & MODEL BIOMEMBRANES

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During two beam-time accesses at CHESS, each of 48 hours duration, we conducted feasibility studies with regard to the prospect of data collection on crystals of several complexes of type 1 human 17b-Hydroxysteroid Dehydrogenase (17b-HSD1) and small crystals of other steroidogenic enzymes, such as human Cytochrome P450 aromatase. We were able to record diffraction under cryogenic conditions and establish the feasibility of data collection on several of these crystals. Two partial data sets were collected on the crystals of equilin- and coumestrol-complexes of 17b-HSD1. Despite being small (< 0.2mm) and thin (< 0.05mm), both these crystals diffracted to about 2.5
resolution. Data sets were about 55-75% complete. More beam time is required to complete the data collection. Our regular application for more beam time has recently received a favorable rating, permitting us to continue with the process. Preliminary structure analyses with these data sets have enabled us to locate equilin and coumestrol molecules in the active site of 17b-HSD1. These results are being presented at the upcoming Endocrine Society meeting in New Orleans.