Increasing microbial resistance to common antibiotics has become a serious threat in maintaining public health. Due to their distinctive features, antimicrobial peptides have become attractive molecules as novel antibiotics. Plants are constantly exposed to attack from a large range of pathogens, and under such conditions, they synthesize antimicrobial peptides as part of their innate defense mechanism. In an effort to identify potential antimicrobial peptides, we have isolated and characterized a novel eight-residue linear peptide from Clitoria ternatea, a perennial plant which belongs to Fabaceae family. Liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) shows a UV-absorbing fraction at 230 nm with a measured molecular mass of 787.4 Da. The sequence of the peptide, QAANSVAK, was derived through de novo approach using tandem mass spectrometric (MS/MS) data obtained after collision-induced dissociation (CID). The sequence was further confirmed through chemical derivatization and proteolysis followed by data-dependent MS/MS analysis. Antimicrobial studies of the nearly homogenous peptide fraction after solid-phase extraction (SPE) show activity against Bacillus subtilis. The peptide bears no sequence similarity with any of the linear peptides isolated thus far from other organisms.
