CRYSTALLIZATION AND PRELIMINARY X-RAY STUDY OF THE VISCUM ALBUM ML1 TOXIN IN ITS NATIVE STATE. N.V.Konareva, A.A.Mikhailov, Institute of Crystallography, Moscow, Russia A.G.Tonevitskii, I.I.Agapov, D.E.Temjakov SRIIMGS, Moscow, Russia A.N.Popov, H.D.Bartunik GBF/MPG, DESY, Hamburg, Germany

The Viscum album ML1 toxin belongs to a group of phytotoxins, such as abrin, ricin, or modeccin, which inhibit the protein synthesis of eukaryotic cells. The toxins of this group are glycoproteins with molecular weights of about 60 kDa. They consist of two subunits, which have their own functions. One of the subunits is lectin with two sites of galactose binding, and the other subunit is a highly specific N-glycosidase - an enzyme, which modifies the 28S RNA-60S ribosomal subunits. The catalitic A (active) and the binding B (binding) subunits are linked into a dimer by a disulfide bond. A handing-drop version of vapor diffusion was used for crystal growth. A precipitating countersolution consisted of ammonium sulfate (in a concentration of 30-35% to a saturated at 20 C solution) and 0.14 M NaCl in a 0.1 M acetate or 0.1M phosphate buffer in a pH range from 4 to 5. The crystallization solution contained equel volumes of a solution of protein (10-13 mg/ml) in one of the above-mentioned buffers and a countersolution. To reduce the number of crystal nuclei, dioxane was added in an amount of 0.01 to 0.02 the volume of the crystallization solution. The X-ray difraction data were collected using the BW6 synchrotron station with a DORIS storage ring (DESY,GBF/MPG, Hamburg, Germany). Intensities were registered using a MARresearch Imaging Plate Scanner. Crystal data are: sp.gr.P6122 (P6522); a=b=110.4 Å, c=309.6 Å. Intensities of 20,683 unique reflections with I>s were measured in the resolution region from20 to 3 Å resolution. The completeness of the data set is 89% and R(I)merge=5.5%.