Aspectos estruturais da toxina da soja (SBTX) e sua participação na defesa vegetal

• Ano de defesa: 2007
• Autor(a) principal: Morais, Janne Keila Sousa
• Orientador(a): Vasconcelos, Ilka Maria
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Bioquímica; Defesa vegetal; Toxinas vegetais; SBTX; Fungos fitopatogênicos; Vegtal defense; Vegetal toxins
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/18175

This work describes the structural characterization of the soybean toxin (SBTX), isolated from seeds by Siebra (2004). In addition, it is discussed the involvement of this protein in plant defense against pathogens. SBTX was isolated using ammonium sulfate fractionation (20-55%), ion exchange and gel filtration chromatographies. Judging by the SDS-PAGE patterns, it was reported to SBTX an apparent molecular mass of 44 kDa, composed of subunits of 27 kDa and 17 kDa, both linked by disulfide bond. NH2-terminal sequencing of electroblotted samples showed that 44 and 27 kDa bands possess identical NH2-terminal amino acid sequences, ADPTFGFTPLGLSEKANLQIMKAYD that differs from that of the 17 kDa band, PNPKVFFDMTIGGQSAGRIVMEEYA. In the fluorescence spectroscopy, excitation of the toxin solution at 280 m gave a maximum emission in 332 m, which is typically for tryptophan residues buried inside the protein. The secondary structure of SBTX by circular dicroism classified this protein as belonging to alpha- and beta class, showing 35% -helix, 13% -sheet and strand, 27% -turn, 25% random coil and 1% aromatic residues and disulfide bonds. SBTX (50 gP/mL) inhibited the spore germination of the filamentous fungi Aspergillus niger and Penicillium herguei, but did not inhibit those of Fusarium solani e F. oxysporum, even at concentrations ten times higher. Nevertheless, SBTX did not interfere in the vegetative growth of the fungus cited above. On the other hand, SBTX slowed the growth of the yeasts Candida albicans and Kluyveromyces marxiannus, but did not have effect on Saccharomyces cerevisiae, suggesting that its effect would be species-specific. The mechanism by which SBTX acts seems to be not related to alteration of the plasmatic membrane permeability. The treatment of soybean seeds with 50 M jasmonic acid, for 24 h, led to remarkable increase in SBTX content. The results suggest that SBTX may have a role in the plant defense strategy against pathogens