Molecular cloning, expression, and characterization of a <italic>Sophora alopecuroides</italic> lectin from <italic>Escherichia coli</italic>

Sophora alopecuroides lectin (SAL) has been isolated from the seeds and confirmed to have antifungal and antitumor activities, and presently the preparation of the natural lectin was cumbersome, time-consuming, and the yield was relatively low for further analysis. In this study, the signal peptide of lectin, the modification sites, and the secondary structure were analyzed, and the three-dimensional structures of SAL were modeled. The gene of SAL was amplified by the reverse transcription polymerase chain reaction, and cloned into the pET-30a vector and expressed in Escherichia coli BL21(DE3) by the induction of isopropyl-beta-d-thiogalactopyranoside. Totally, 400 mg of recombinant SAL (rSAL) was purified from 1 l of bacterial culture through Ni-NTA agarose column and the purity reached 95%. The recombinant protein was further confirmed by western blot using rSAL-specific antibody. The biological activity analysis results showed that rSAL exclusively bound to d-galactose and had universal hemagglutinating activities to human A, B, O, and AB, and rabbit and mouse erythrocytes. rSAL also inhibited the growth of fungi, the proliferation of cancer cells, and the HIV-I reverse transcriptase activity. In conclusion, this study indicates that rSAL can be produced in large quantities in the prokaryotic expression system and the recombinant protein still retains the various biological activities, which will make the large-scale production of SAL recombinant protein at dramatically reduced cost possible.