Six Polymorphic Crystal Forms of α-Cobratoxin.

Six different crystal forms of the long neurotoxin α-cobratoxin isolated from the venom of Naja naja siamensis have been obtained and the conditions for their crystallisation are described. Heavy atom derivatives for two of these forms have been prepared and have proven suitable for high-resolution X-ray studies and, with one of them, a 0.28-nm resoution structure has been determined. All but one of the crystal forms were grown between pH 2 and pH 3. Two novel suggestions are made which may be applicable to other protein crystallisation studies. One involves cocrystallisation with mercurous iodide and the other describes a two-step microdialysis procedure. first against salt solution, followed by analysis against poly(ethylene glycol). [ABSTRACT FROM AUTHOR]