Cloning, Prokaryotic Expression, Antibody Preparation And Tissue Distribution Studies Of Li Protein From Lampetra Morii Berg

Lamprey, the representative of jawless vertebrates, is the oldest extant species with theadaptive immune system. Its immune molecules of adaptive immune system are significantlydifferent from Jawed vertebrates, such as antigen specific receptors and leukocyte antigens etal. Which immune molecules, however, are engaged in killing of exogenous cell in lampreyhave not been reported.Previous study found a kind of cytotoxic protein in lamprey, and named ’Li protein’.Utilized the result of mass spectrometry analysis, this research gets the full-length cDNA ofLi protein(1120bp) by molecular biological techniques. Bioinformatics analysis indicatedthat Li protein contains tow domains. The Jacalin_like domain is located in N-terminal andAerolysin domain is located in C-terminal. The spatial structure of Li protein mainlycomposed of β-sheet. Both from primary structure and spatial structure, it is significantdifferent between Li protein and cytotoxic molecules of mammalian. Further studies foundmany Li protein clones in sea lamprey genome, and they share highly polymorphic. Theseresults imply Li protein could have the capable of specifically recognizing its target cell.The construction of prokaryotic expression system used to obtain recombination Liprotein. Purification of rLi protein as antigen to immunize New Zealand rabbits, preparationrabbits anti-Li protein polyclonal antibody. Tissue distribution analysis indicates that Liprotein is mainly located in lamprey immune body and leukocyte. Nevertheless, plasmasamples are devoid of Li protein and Li protein expression by erythrocyte is higher thanleukocyte. These features show a striking discrepancy with adaptive immune system ofmammalian.In hundreds of millions of years, adaptive immunity in vertebrates has been tremendouschanges in the course of evolution. Only retrospect more primitive jawless vertebrates, tostudy the important immune molecules and immune mechanism, could reveal the origin andevolution of the adaptive immune system. This study on cytotoxic molecule of lampreyprovides a novel insight into the origins of adaptive immunity.