Antimicrobial and anticancer potential of low molecular weight polypeptides extracted and characterized from leaves of Azadirachta indica

Low molecular weight antimicrobial polypeptides were extracted and purified from the young fresh leaves of Azadirachta indica (neem). The total protein extracted was precipitated with 15% TCA-Acetone. The total purified proteins yielded from the two extraction methods were 122.33 ± 2.21 and 115.09 ± 1.88 mg/g of the total fresh weight. The SDS-PAGE analysis identified the presence of eight low molecular weight polypeptide bands. The antimicrobial activity of the resolved bands was detected by Polyacrylamide gel-Agar overlay diffusion assay (PAG-ADA). Their broad-spectrum bactericidal activity was confirmed using the same technique and found three low molecular weight bands from 11 to 14 kDa collectively exhibiting superior bactericidal activities against Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermis, Enterococcus faecalis, Pseudomonas aeruginosa and fungicidal activity against Candida tropicalis. The FTIR spectrum of the protein bands depicted the presence of hydroxyl and carbonyl groups in the protein bands. These polypeptides were characterized by MALDI-TOF/TOF analysis. Further, the purified protein extract was found to be active against HELA, BT-549 and Neuro-2a cell lines with IC50 value of 74.03 ± 2.31, 64.82 ± 1.64, 238.32 ± 2.12 and 109.94 ± 2.96, 59.61 ± 0.75 for 24 h and 48 h, respectively. The results of present study indicate that these polypeptides exhibit broad spectrum antimicrobial and anticancer activity and can therefore be explored for their therapeutic potential.