Purification, crystallization and initial structural solution of a new α-like toxin with cardiac toxicity from scorpion Buthus martensii Karsch

An alpha-like toxin named BmK M7 active on both mammals and insects has been purified from the venom of scorpion Buthus martensii Karsch (BmK) recently. The electrophysiological experiments showed that M7 can bind to human cardiac Na+-channel and modify its normal properties, hence can be considered as a cardiotoxin. Single crystals of M7 have been obtained by hanging-drop vapor diffusion method using ammonium sulfate as precipitant in Tris-HCl buffer at pH 8.5. A data set to 1.40 Angstrom resolution was collected using synchrotron radiation and CCD detector in Photon Factory in Japan. Data analysis showed that the crystals belonged to space group P3(1)21/P3(2)21, with cell dimensions a=b=32.76 Angstrom, c=176.82 Angstrom. Assuming two molecules per asymmetric unit, the V-m value is 1.92 Angstrom(3)/Da. The initial structural analysis was carried out by molecular replacement, which showed the correct space group (P3(1)21), and the orientations and positions of the two molecules in the asymmetric unit.