Estudo conformacional de proteínas por espectroscopia Raman laser e de absorção no infravermelho: toxina γ de tityus serrulatus e fosfolipases A2 de crotalus durissus terrificus e de pâncreas de porco e seu zimogênio / Conformational study of proteins by Raman laser and infrared absorption spectroscopies: gamma-toxin from Tityus serrulatus and phospholipases A2 from Crotalus durissus terrificus and from pig pancreas and its zymogen

AUTOR(ES)

Elizabeth Pinheiro Gomes Areas

DATA DE PUBLICAÇÃO

1990

RESUMO

Raman and infrared spectroscopies were used to investigate conformational features of some proteins of biological interest, in what concerns structural aspects of their polypeptide backbones and microenvironments of certains amino acid residue side-chains. The work has been divided in two groups as related to the systems studied: a) Toxin γ from the venom of Brazilian scorpion Tityus serrulatus. The vibrational analysis has revealed that the protein polypeptide backbone consists of different secondary structures, with predominance of β-sheet, followed by unordered structure and α-helix, with some evidence of β-turns. A gauche-gauche-gauche (ggg) conformation for the CCSSCC fragments of the four dissulfide bridges has been detected. The intensity of the Tyr Raman doublet at 853 and 828 cm-1 indicated that 4 out of the 5 Tyr residues are exposed at the molecular surface. External localization of the 3 Trp residues has also been indicated. Under a qualitative point of view, conformational features of the toxin the amorphous solid state and in solution were virtually the same. B) Crotalus durissus terrificus and porcine pancreatic phospholipases A2. Conformational changes were detected for the phospholipases molecules as a consequence of different conditions such as change of physical state, presence of certain ionic species and interaction with a model substrate analog and with the substrate itself. Amorphous and crystalline solid pancreatic phospholipases presented discrepant conformational features. Conformational transitions were detected for the pancreatic zymogen → phospholipase A2 transformation and different secondary structures contents were observed for the toxic and the non toxic phospholipase melecules. All those structural changes heve been shown to involve primarily the architecture of the polypeptide backbone rather than the conformation of amino acid residue side-chains. Disulfide bridges have shown consistently a ggg conformation which has not been disturbed by any of the experimental conditions employed. The external occurrence of tryptophan residues has been a common feature for the systems assayed, as well as the predominant localization of tyrosine residues in hydrophylic environments, probably at the molecular surface.

ASSUNTO(S)

biochemistry bioqímica espectroscopia raman fosfolipase phospholipase proteínas proteins raman spectroscopy toxin toxina

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