Purification, crystallization and preliminary X-ray analysis of the disintegrin contortrostatin from Agkistrodon contortrix contortrix snake venom

Disintegrins are cysteine-rich RGD-containing peptides that block tumor-cell implantation and angiogenesis. Contortrostatin, a homodimeric disintegrin (64 residues in each chain) from southern copperhead snake venom, has been purified to homogeneity and crystallized. Initial attempts at crystallization led to a form grown from polyethylene glycol (PEG), which crystallizes in the orthorhombic space group C222₁, with unit-cell parameters a = 57.39, b = 139.55, c = 78.98 Å, and diffracts to a resolution limit of 3.2 Å. Very recently, a new crystalline form of the title protein has been obtained grown from ammonium sulfate [(NH₄)₂SO₄] as a precipitant having a space group of P2₁2₁2₁, with unit-cell parameters a = 37.52, b = 59.93, c = 121.37 Å. These improved crystals diffract to a resolution limit of 1.7 Å.