Interaction of azadirachtin with the lipid-binding domain: Suppression of lipid transportation in the silkworm, Bombyx mori

This study investigates the effects of the insect growth regulator azadirachtin on lipid transportation to the ovary of the silkworm, Bombyx mori. Lipids are hydrophobic in nature and require a carrier for circulation in the blood. Protein-lipid interactions play a vital role in lipid transport, thereby keeping the system balanced. In general, lipids bind to lipoproteins in a specific region called the lipid-binding domain (LBD). In this study, B. mori apolipophorin amino acid sequences were retrieved from NCBI and the LBD was identified. The LBD structure was predicted by (PS)(2) and validated in ProSA. The LBD structure was docked with DMPC, POPC and sphingomyelin by SwissDock, each binding with GLN 171, ASN 162, and ASN 160 and 162, respectively. Interestingly, azadirachtin binds with ASN 160 and 162 and GLN 171, which shows that lipids and azadirachtin are binding with the same amino acid residues in the LBD. Later, this result was confirmed with wet lab work using a fluorescent phospholipid probe. Azadirachtin binding with the LBD was indirectly proportional to the fluorescent lipid binding. These results suggest that azadirachtin binds with the LBD instead of the lipids and interrupts the protein-lipid interaction, leading to the suppression of lipid transportation to the ovary.