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Antimicrobial peptides (AMPs) are produced by a range of organisms as a first line of defense against invaders or competitors. Owing to their broad antimicrobial activity, AMPs have attracted attention as a potential source of chemotherapeutic drugs. The increasing prevalence of infections caused by Candida species as opportunistic pathogens in immunocompromised patients requires new drugs. Lecythis pisonis is a Lecythydaceae tree that grows in Brazil. The AMPs produced by this tree have not been described previously. We describe the isolation of 12 fractions enriched in peptides from L. pisonis seeds. Of the 12 fractions, at 10 μg/ml, the F4 fraction had the strongest growth inhibitory effect (53.7%) in Candida albicans, in addition to a loss of viability of 94.9%. The F4 fraction was separated into seven sub-fractions by reversed-phase chromatography. The F4.7' fraction had the strongest activity at 10 μg/ml, inhibiting C. albicans growth by 38.5% and a 69.3% loss of viability. The peptide in F4.7' was sequenced and was found to be similar to plant defensins. For this reason, the peptide was named L. pisonis defensin 1 (Lp-Def1). The mechanism of action that is responsible for C. albicans inhibition by Lp-Def1 includes a slight increase of reactive oxygen species induction and a significant loss of mitochondrial function. The results described here support the future development of plant defensins, specifically Lp-Def1, as new therapeutic substances against fungi, especially C. albicans., (© The Author 2015. Published by ABBS Editorial Office in association with Oxford University Press on behalf of the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences.)

Plant defensins are cationic peptides that are ubiquitous within the plant kingdom and belong to a large superfamily of antimicrobial peptides found in several organisms collectively called defensins. The primary structure of these peptides includes 45 to 54 amino acid residues with considerable sequence variation. At the level of three-dimensional structure, they are small and globular, composed of three anti-parallel β-sheets and one α-helix, which is highly conserved among these peptides. The three-dimensional structure is stabilized by four disulfide bridges formed by eight strictly conserved Cys residues. Two of these bridges compose the Cys-stabilized α-helix β-strand motif, which is found in other peptides with biological activities. Plant defensins present numerous biological activities, such as inhibiting protein synthesis, ion channel function and α-amylase and trypsin activity; impairing microbial, root hair and parasitic plant growth; mediating abiotic stress and Zn tolerance; altering ascorbic acid redox state; stimulating sweet taste sensation; serving as epigenetic factors; affecting self-incompatibility; and promoting male reproductive development. Some of these biological activities, such as microbial growth inhibition and sweet taste induction, coupled with a scaffold that provides these peptides with incredible physicochemical resistance to harsh environments and the potential for simple amino acid substitution, raise the opportunity to improve the function of defensins or introduce new activities, endowing these peptides with great biotechnological and medical significance. This review will cover the biological activities and roles of plant defensins and will focus on their application in the field of biotechnology.