THE 3.0 ANGSTROM PROJECTION STRUCTURE OF MICROSOMAL GLUTATHIONE TRANSFERASE AS DETERMINED BY ELECTRON CRYSTALLOGRAPHY OF P2(1)2(1)2 2-DIMENSIONAL CRYSTALS

Two-dimensional crystals of rat microsomal glutathione transferase wer e grown during dialysis of detergent-solubilized enzyme after addition of a small amount of phospholipid. The crystals had two-sided plane g roup symmetry p2(1)2(1)2 with a calibrated unit cell size of a=91.90 A ngstrom, b=90.83 Angstrom. Electron diffraction patterns were recorded showing significant reflections extending to 3.0 Angstrom. A combinat ion of these structure factor amplitudes with phases from high-resolut ion images following image processing was used to calculate a projecti on may of the protein. The asymmetric unit of the structure consists o f three microsomal glutathione transferase molecules. The local 3-fold axis at the center of the trimer is delineated by six parallel alpha- helices, two from each monomer. The two helices differ significantly i n their respective projection structure. The inner helical core of the trimer is partly surrounded by elongated domains with extensions towa rds the helices and which contain resolved density maxima at a spacing of 4 to 5 Angstrom. A well-defined strong peak is localized close to the elongated domain and at a distance of about 9.5 Angstrom from two of the inner helices. (C) 1997 Academic Press Limited.