Evolution, adaptation and immune functions of fish F-type lectins. The novelty of FBL from Trematomus bernacchii (Boulenger, 1902)

Abstract

Lectins are a protein family, present in almost all living organisms and involved in different biological pathways, such as immune responses. The Fucose Binding Lectin (FBL), constitute the latest lectin family identified and characterized in fishes. The FBL family is constituted by a large number of proteins exhibiting multiples of the F-type motif, either tandemly arrayed or in mosaic combinations with other domains. In an early step a FBL has been isolated and characterized from serum of the Antarctic fish Trematomus bernacchii by affinity chromatography on fucose-agarose column. A clear Bacterial agglutinating activity (BA) towards different bacteria strains (Escherichia coli, Kokuria rhizophyla and Bacillus subtilis) and Hemagglutinating activity (HA) toward rabbit erythrocytes was induced from the serum as well from the purified protein and thus confirm its involvement in host pathogen interactions. In SDS-PAGE analysis, the FBL exhibited an apparent molecular weight of 30 kDa. This data is confirmed from the sequence of the F lectin recognised on the T. bernacchii transcriptome. The sequence shows a similar and coherent structure with a supposed Mw 32.16 kDa and an isoelectropoint of 5.21. Furthermore, sequencing the N-terminus confirmed the identity of the sequence runned on SDS PAGE and blotted on PVDF membrane. The HA activity was analyzed at different temperatures and it was maintained also at the physiological living low temperatures of this fish habitat (close to 0 °C). Therefore, in order to identify trends linked to cold adaptation in Antarctic fish, we present our hypothesis on the conformational change determined by the aminoacidic substitutions respect the others fish fucolectins living in warmer water on the light of the general phylogenetic scenario including the new preliminary data on sharks FBL