A METHOD FOR PROCESSING DIFFRACTION DATA FROM TWINNED PROTEIN CRYSTALS AND ITS APPLICATION IN THE STRUCTURE DETERMINATION OF AN FAD NADH-BINDING FRAGMENT OF NITRATE REDUCTASE

A general method to deconvolute oscillation data sets from twinned pro tein crystals to a corresponding single crystal data set has been deve loped and applied to diffraction data measured from crystals of a frag ment containing the FAD- and NADH-binding domains of nitrate reductase . The procedure allows straightforward processing of diffraction data from twinned crystals. Typically, R(merge) values of reduced data sets from the nitrate reductase crystals after deconvolution are about 0.0 6 compared to 0.13 and higher before deconvolution. Based on these dec onvoluted data sets, the structure of the FAD- and NADH-binding domain s of nitrate reductase could be solved successfully. The result indica tes that crystal twinning does not necessarily prevent crystallographi c structure determination.