Preliminary X-ray investigation of variant-2 scorpion toxin from Centruroides sculpturatus Ewing. Evidence of a reversible transition between crystal forms.

Crystals of Variant-2 scorpion toxin have been grown using seeding techniques from 30% 2-methyl-2,4-pentanediol at pH 9.2 and T = 4 degrees C. These crystals display a temperature-dependent, reversible phase transition near room temperature. The apparent space group for the high-temperature form is P3121 or P3221 with a = 48.8(1) A and c = 43.7(1) A, and with one molecule per asymmetric unit. At lower temperature, the crystals undergo a phase transition in which the space group remains the same but with c' (approximately equal to 2c) = 86.1(1) A. In addition, the low-temperature form displays several weak, diffuse reflections that correspond to a tripling of the a axis. The high-temperature form diffracts beyond 1.8-A resolution and appears to be suitable for a complete structural study.