Purification, N-terminal sequencing, crystallization and preliminary X-ray diffraction analysis of atratoxin, a new short-chain α-neurotoxin from the venom of Naja naja atra

Atratoxin, a new α-neurotoxin purified to homogeneity by a series of liquid chromatographies from the venom of Naja naja atra (mainland Chinese cobra), is a small single-polypeptide alkaline protein with a pI of about 9.5 and molecular weight of 6952 Da estimated by mass spectrometry. Although the sequencing of the N-terminal 15 residues (LECHNQQTTQQPEGG) shows that this neurotoxic protein contains most of the residues, especially at the conserved positions, of the consensus sequence of short-chain α-neurotoxins, the natural mutations in the N-terminal Loop-1 presented by the sequence alignment may have structural or functional implications for the interactions between α-neurotoxins and related receptors. Single crystals of atratoxin have been grown from drops containing the necessary Cu²⁺ ions by the conventional hanging-drop vapour-diffusion method. The crystals diffract X-rays to 1.6 Å resolution and belong to space group C222₁, with unit-cell parameters a = 47.36, b = 47.83, c = 91.31 Å, corresponding to a volume-to-mass ratio of 1.85 ų Da⁻¹ and two molecules in each asymmetric unit.