Structures And Functions Of Two Toxins From The Chinese Bird Spider Of Ornithoctonus Huwena

Abstract l:The Chinese bird spider, Ornithochoctonus huwena, distributed in the hilly areas of Yunnan and Guangxi in the south of China, was recently identified as a new species and is one of the most venomous spiders in China. In our previous work, we have demonstrated that 0. huwena venom contains a mixture of compounds with different types of biological activities. Most of them are neurotoxins, such as HWTX-1, -II ,-III, IV.Huwentoxin XI (HWTX~XI),a serine protease! inhibitor, consists of 55 amino acid residues with three disulfide bridges. The toxin was isolated from the venom of the Chinese spider Ornithochoctonus huwena by ion-exchange chromatogram -phy and reverse phase high performance liquid chromatography.The jmolecular weight of HWTX-XI is 6166. 2, determined by MALDI-TOF mass spectrometry ,which is identical with thecalculated mass based on the complete amino acid sequence of NH2-IDTCRLPSDRGRCKASFERWYFNGRTCAKFIYGGCGGNGNKFPTQEACMCAKA - COOH, determined by automatic Edman degradeation .The inhibition of trypsin by HWTX-XI was competetive ,with a ki value of 2. 938 X 108mol/L (BAPNA as substrate), which is determined by using a U-2000 spectrophotometer instrument (HITACHI , Japan) .The binding properties of HWTX-XI on trypsin and a -chymotrypsin were measured by a BIAcore binding assay system. Results showed that HWTX-XI could bind to trypsin with a dissociation constant of 1. 23 X 10-10mol/L, and to a -chymotrypsin with a dissociation constant of 1. 14 X 10-7mol/L . Inhibition profiles of trypsin by HWTX-XI revealed a 1:1 binding stoichiometry between this inhibitor and trypsin.Huwentoxin XI also have a strong biological activity with a LD5n=256 u g/kg when injected into the fourth ventricle of the adult mouse brain.