A NOVEL FAMILY OF SMALL CYSTEINE-RICH ANTIMICROBIAL PEPTIDES FROM SEED OF IMPATIENS-BALSAMINA IS DERIVED FROM A SINGLE PRECURSOR PROTEIN

Four closely related peptides were isolated from seed of lmpatiens bal samina and were shown to be inhibitory to the growth of a range of fun gi and bacteria, while not being cytotoxic to cultured human cells, Th e peptides, designated Ib-AMP1, Ib-AMP2, Ib-AMP3, and Ib-AMP4, are 20 amino acids long and are the smallest plant-derived antimicrobial pept ides isolated to date, The Ib-AMPs (I. balsaminn antimicrobial peptide s) are highly basic and contain four cysteine residues which form two intramolecular disulfide bonds. Searches of protein data bases have fa iled to identify any proteins with significant homology to the peptide s described here, Characterization of isolated cDNAs reveals that all four peptides are encoded within a single transcript, The predicted Ib -AMP precursor protein consists of a prepeptide followed by 6 mature p eptide domains, each flanked by propeptide domains ranging from 16 to 35 amino acids in length, Such a primary structure with repeated alter nating basic mature peptide domains and acidic propeptide domains has, to date, not been reported in plants.