Purificação e caracterização bioquímica de lectinas ligantes de galactose isoladas de invertebrados marinhos

Abstract

Lectins, which are found in all living organisms, are sugar-binding proteins that differ from immunoglobulins and glycoenzymes because they are not produced as an adaptive immune response, and they contain no site for the enzymatic modification of their ligands. Lectins have been studied for more than a century because of their ability to decipher glycocode. Excepting Crustacea (Arthropoda) and Bivalvia (Mollusca), marine invertebrates have been poorly studied compared to the distribution and presence of lectins. This work aimed to isolate lectins from groups of invertebrates with poorly studied, biochemically characterize such lectins and to evaluate its effect on the formation of bacterial biofilms. Lectins were isolated from the sponge Aplysina lactuca (ALL), the eggs gastropod Aplysia dactylomela (ADEL) and the sea urchin Echinometra lucunter (ELEL). ALL is a dimer formed by two identical 16 kDa subunits linked by disulfide bonds with affinity for lactulose, lactose and mucins. Its primary structure is similar to the Axinella polypoides lectin and its secondary structure is formed mainly by β-sheet. ADEL is a high mannose glycoprotein formed by two identical 27 kDa subunits linked by disulfide bonds. Its primary structure showed similarity with other lectins obtained from aplysid eggs. The secondary structure of ADEL is rich in β-sheet and sensitive to the presence of carbohydrates. ADEL showed affinity for several galactosides, especially for galacturonic acid (Ka = 1,5 x 107 M-1). The three-dimensional ADEL model reveals a new carbohydrate recognition domain. ELEL is a rhamnose binding lectin formed by two 11 kDa subunits linked by disulfide bonds. ELEL showed affinity for carbohydrates containing the same orientation in the hydroxyls of C-2 and C-4 as galactose. Its primary structure was similar to lectins found in eggs of sea urchins and fish. The three-dimensional ELEL structure model suggests the predominance of β-sheets in a β-sandwich domain. Ab initio calculations suggest the interaction of ELEL with a common receptor in tumor cells, Gb3. In addition, the three lectins showed ability to agglutinate bacteria and / or inhibitory effect of the growth of bacterial biofilms. In conclusion, this work reveals that invertebrates represent an excellent source of new galactose binding lectins and presenting inhibitory effect in the bacterial growth and/or antibiofilm, so these new lectins may be useful as biotechnological tools in the near future.