Effects of the aspartic protease inhibitor from Lupinus bogotensis seeds on the growth and development of Hypothenemus hampei: an inhibitor showing high homology with storage proteins.

The coffee berry borer Hypothenemus hampei is a pest that causes great economic damage to coffee grains worldwide. Because the proteins consumed are digested by aspartic proteases in the insect's midgut, the inhibition of these proteases by transferring a gene encoding an aspartic protease inhibitor from Lupinus bogotensis Benth. to coffee plants could provide a promising strategy to control this pest. Five aspartic protease inhibitors from L. bogotensis (LbAPI) were accordingly purified and characterized. The gene encoding the L. bogotensis aspartic protease inhibitor (LbAPI), with the highest inhibitory activity against H. hampei, was expressed in Escherichia coli and the purified recombinant protein (rLbAPI), with a molecular mass of 15 kDa, was subsequently assessed for its ability to inhibit the aspartic protease activity present in the H. hampei midgut in vitro, as well as its effects on the growth and development of H. hampei in vivo. The in vitro experiments showed that rLbAPI was highly effective against aspartic proteases from H. hampei guts, with a half maximal inhibitory concentration (IC50) of 2.9 μg. The in vivo experiments showed that the concentration of rLbAPI (w/w) in the artificial diet necessary to cause 50% mortality (LD50) of the larvae was 0.91%. The amino acid sequence of LbAPI had high homology (52-80%) to the seed storage proteins, vicilin and β-conglutin, suggesting that this protein was generated by evolutionary events from a β-conglutin precursor. Based on these results, LbAPI may have a dual function as storage protein, and as defense protein against H. hampei. These results provide a promising alternative to obtain a coffee plant resistant to H. hampei.