Purification and partial characterization of a lectin from the prawn Macrobrachium americanum (Decapoda, Palaemonidae)

Lectins play relevant roles in the innate immunity of invertebrates. From the haemolymph of the prawn Macrobrachium americanum Spence Bate, 1868 we purified by affinity chromatography a lectin (MaL) composed of three subunits (86.6, 66.2 and 42.7 kDa), as identified by SDS-PAGE. It is mainly composed of Gly, Ser and Arg, and Ala, Glx and Lys in a minor proportion; it lacks Trp, Cys and carbohydrates. MaL agglutinated mainly rat erythrocytes, rabbit or mouse erythrocytes were agglutinated with lower capacity; whereas erythrocytes from human or other species were not agglutinated. It is specific for N-acetyl-neuraminic acid (sialic acid), N-acetyl-d-glucosamine and N-acetyl-d-galactosamine; sialylated fetuin and bovine submaxillary mucin are also powerful inhibitors of the lectin's activity. After physical daily manipulation of prawns for 7 days, the lectin concentration and the specific activity (haemagglutinating activity/protein concentration) increased more than four-fold over the control group (those animals that had not been manipulated until bleeding), suggesting that increased lectin concentration and activity after manipulation could be considered as markers of stress.