Estudos estruturais de uma lectina da secreção da glândula parotóide de Rhinella schneideri

Abstract

Lectins are defined as proteins or glycoproteins that have at least one non-catalytic domain able to recognize carbohydrates and interact with them in a reversible and specific way. Lectins have been studied for more than a century and are present in various organisms such as plants and animals, and have been found in the cytoplasm, nucleus and cell membranes of the most diverse animal cells. Animal lectins are classified into families, according to their function structural characteristics. The presence and distribution of lectins in the secretions of Amphibians` most diverse glands have been little studied. The objective of this work was to determine structural aspects of a galactose binding protein and its derivatives present in the secretion of the paratoid gland of the frog Rhinella schneideri. Specimens of R. schneideri were collected in the city of Floriado, Piauí. Protein was isolated by classical methods of protein chemistry. This lectin is a heterogeneous protein because it has subunits of different molecular weight with affinity for 4-nitrophenyl-α-galactoside, α-lactose, β-lactose, lactulose and mucin type 2. Through size exclusion chromatography the protein presented two subunits with different molecular weight, 64 kDa and 40 kDa. The secondary structure content was analyzed by circular dichroism. The protein consists mainly of β-sheets, as has been reported for other animal lectins. The protein`s native form preseted to 62.5°C as melting temperature, evidencing that it has thermal stability in front of high temperatures. The protein was subjected to proteolytic cleavage. The peptides of each subunit were partially sequenced, and showed no similarities to any of the proteins available in the databases, but the peptides overlap when one subunit is related to the other, evidencing that the protein is heterogeneous, formed by the subunits. According to the above, a protein specific for galactose and derivatives was isolated from the secretion of the paratoid glands of R. schneideri and partially characterized as the structure.