Características estruturais e funcionais de lectinas de Diocleinae

• Ano de defesa: 1996
• Autor(a) principal: Ramos, Márcio Viana
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Bioquímica
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/43019

The structural and functional features of lectins from sub-trib e Diocleinae were analysed by different biochemical and computational techniques. The five lectins studied showed similar properties and are in agreement with that from ConA, the most celebrated lectin from this sub-tribe. The fine specificity of the lectins to simple and complex carbohydrates, as well as glycoproteins, showed rather differences in affinity of each lectin and their specific ligands. These differences were also evidenciated when the real time interaction between the lectins and some glycoproteins was measured by surface plasmon ressonance. All tested lectins, including ConA lectin, exhibited expresive immunological identity as determined by ELISA experiments, using anti-ConA and anti-DGL polyclonal antibodies. The secondary structure of the lectins avaliated by Hydrophobic Cluster Analysis and Hydropatic Profile indicated similar hydrophobic and hydrophilic core in equivalent regions along their sequences, thus suggesting similar general features on their secondary structure. The molecular modelling of ConBr, ConM, DGL and DLEL lectins was performed from the crystallographic coordenates of ConA. Their three-dimentional models suggest that these lectins constitute a family of proteins which have been strongly conserved structures during evolution and that, associated to their identical specificity, indicates that they should play the same biological functions in their plants. The comparative study of the monosaccharide binding-site of the modelled lectins with differents monosaccharides, suggest that conformational changes in the protein structure is required to make possible the lectin-ligand interaction. The role played by C3, C4 and C6 Carbon could also be evaluated. Although the C2 Carbon is not directly envolved in interactions, the affinity of the complex is altered, according to the chemical group bound to C2. The significance of a, b and y subunits in the inhibitory activity by glycoproteins, including ConA lectin, was investigated. Although ConA a subunit had been sucessfully isolated, some lectins were resistent to the same treatment. Results from the inhibition tests showed that different proportions of the subunits (aby) in the composition of the quaternary structure could explain the differences in affinity among lectins. Although the crystal structure of ConA lectin suggests a tetrameric structure for this protein, in solution, all lectins from Diocleinae avaliated by gel filtration cromatography on FPLC system, exhibited predominantly dimeric forms at neutral and basic pH values, and a monomereric form at low pH, indicating an equilibrium mixture of monomeric, dimeric and tetrameric forms depending on pH.