A series of bioactivity-variant neurotoxins from scorpion Buthus martensii Karsch: Purification, crystallization and crystallographic analysis

Three bioactivity-variant neurotoxins, BmK M1, M4 and M8, have been purified from Chinese scorpion BmK venom. They possess distinct toxic activities against mice in vivo. These proteins also have different electrostatic properties. The relative toxicities for BmK M1, M4 and M8 are 13.3:2.5:1 which, surprisingly, correspond to their respective pI values ranging from basic to acidic 9.01, 7.53 and 5.30, respectively. They have been crystallized in different crystal forms as orthorhombic, hexagonal and monoclinic, respectively. These crystals can diffract to 1.2 (BmK M1), 1.3 (BmK M4) and 1.8 Å (BmK M8) resolution and have been used in data collection. These toxins produced by natural mutagenesis or gene divergence should represent functionally distinct states, thereby forming a valuable system for studying structure-function relationships. The unusual relatively acidic component that first appeared in this series also provides a new concept for a more comprehensive understanding of scorpion neurotoxins.