1Departamentos de Farmacologia e ²Bioquímica-Imunologia, ICB, UFMG, Belo Horizonte, MG, Brazil.

E-mail: decarval@mono.icb.ufmg.br

The venom of the spider Phoneutria nigriventer contains a collection of neurotoxics peptides that are known to interfere with the function of voltage gated channels (Cordeiro et al.,1995). Initial purification procedures permitted the isolation of four main toxic fractions with distinct pharmacological properties (Resende et al., 1991). These studies showed that the PhTx2 fraction, which is responsible for the most prominent effects of the crude venom, contained at least 9 distinct components. It seems an important approach characterize the components at the molecular level. Towards this end, we have prepared a cDNA library from Phoneutria nigriventer venom gland to clone the cDNAs enconding neurotoxins related to Tx2-5.

A cDNA library from Phoneutria nigriventer venom gland has been prepared and used to identified the cDNA of one isoform of the toxin Tx2-5 called Pn2-5A (Kalaphotakis et al., 1995), this isoform showed 94% sequence homology to the Tx2-5 toxin and 92% to Pn2-1, other isoform cloned by our group. The cDNA from the isoform Pn2-5A was used to build a radioactive probe, and screen the cDNA library. The positive clones isolates from the library were purified and sequenced suggest the identification of new isoforms, pointing for the existence of a large number of toxin families in the venom of the spider P. nigriventer. All this different isoforms provides a wide spectrum of the venom, guaranteeing their versatility of action in different organisms.