In Silico Studies and Functional Characterization of a Napin Protein from Seeds of Brassica juncea

<ns2:p>Pathogenicity related proteins and peptides have been utilized as natural substitute to control phytopathogenic microbes and insects. A 15 kDa Napin protein from seeds of Brassica juncea was identified and characterized. SDS-PAGE separated native 15 kDa protein into two peptidic molecular masses of approximately 10 kDa and 5 kDa under reduced conditions. Ammonium sulfate precipitation (70%) followed by gel filtration chromatography provided a highly purified protein. A homology model of B. juncea Napin (BjN) was developed by using PDB ID: 1SM7 as the template structure. BjN predicted model showed conserved topology and disulfide bond patterns similar to rapeseed napin; which however, possessed a long hyper variable region between helices III and IV. An extra internal repeat of residues 77-87 has been predicted as unique segment of BjN predicted model. BjN exhibited inhibitory activity against growth of different pathogenic bacterial and fungal strains assessed by disc diffusion method. A 60 µg/disc concentration of the purified protein exhibited strong antibacterial activity towards Xanthomonas oryzae, Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, P. syringae and Bacillus subtilis. Similarly, BjN (90 µg/disc) significantly inhibited the mycelial growth of Aspergillus flavus and Fusarium oxysporum. BjN also showed good insecticidal potential against Sitophilus oryzae and Tribolium castaneum at a dose of 1.5 mg. The strong antimicrobial as well as insecticidal activity shown by the protein signified its potential as arsenal of antimicrobial and insecticidal agents.</ns2:p>