A novel synthetic peptide from a tomato defensin exhibits antibacterial activities against Helicobacter pylori M. M. Rigano, a A. Romanelli, b A. Fulgione, a N. Nocerino, a N. D’Agostino, c C. Avitabile, b L. Frusciante, d A. Barone, a F. Capuano e and R. Capparelli a * Defensins are a class of cysteine-rich proteins, which exert broad spectrum antimicrobial activity. In this work, we used a bioinformatic approach to identify putative defensins in the tomato genome. Fifteen proteins had a mature peptide that includes the well-conserved tetradisulfide array. We selected a representative member of the tomato defensin family; we chemically synthesized its g-motif and tested its antimicrobial activity. Here, we demonstrate that the synthetic peptide exhibits potent antibacterial activity against Gram-positive bacteria, such as Staphylococcus aureus A170, Staphylococcus epidermidis, and Listeria monocytogenes, and Gram-negative bacteria, including Salmonella enterica serovar Paratyphi, Escherichia coli, and Helicobacter pylori. In addition, the synthetic peptide shows minimal (<5%) hemolytic activity and absence of cytotoxic effects against THP-1 cells. Finally, SolyC exerts an anti-inflammatory activity in vitro, as it downregulates the level of the proinflammatory cytokines TNF-a and IFN-g. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd. Supporting information may be found in the online version of this article. Keywords: antimicrobial peptide; defensin; tomato; Helicobacter pylori Introduction Attention towards new antimicrobial agents is growing because of the rising of antibiotic and multidrug bacterial resistance [1,2]. Particular interest is devoted to the development of novel antibio- tics against Helicobacter pylori, a Gram-negative bacterium that chronically infects the gastric mucosa of more than half of the human population and sometimes causes severe diseases, such as gastric cancer [3]. H. pylori LPS shows extremely low endotoxic activity, compared with typical Gram-negative LPSs, allowing it to establish chronic colonization without causing a systemic inflam- matory response [4]. Currently, the prevalent approach for H. pylori eradication is based on antibiotic treatment. However, antibiotics cause serious effects on the intestinal microflora and induce antibiotic-resistant strains [5]. Antimicrobial peptides are cationic molecules of the innate immune system and represent a valid defense mechanism against infections because of their broad spectrum antibiotic activity and low eukaryotic cell toxicity. In addition, they rarely induce bacterial resistance [1,6]. Defensins are the only class of peptides in the innate immune response that is conserved among plants, inverte- brates, and vertebrates [7]. They are cysteine-rich proteins with a common three-dimensional structure rich in b-sheets [1]. Plant defensins (originally classified as g-thionins, [8]) are small, basic, highly stable proteins with antifungal and antibacterial properties [8,9]. Their structure resembles that of insect and mammalian defensins, corroborating the idea that all defensins evolved from a single precursor [8]. Indeed, Yount and Yeamen [10] identified a conserved g-core motif (GXCX 3-9 C) – composed of two antiparallel b-sheets and an interposed loop [10] – in disulphide-containing AMPs from several phylogenetically diverse organisms. This motif has a net cationic charge and can be found in other host-defense polypeptides with antimicrobial activity, such as venoms, toxins, or microbicidal chemokines [11]. The recent release of the tomato genome sequence [12] facili- tates the identification of genes encoding proteins with potential antimicrobial activity. In this work, we used bioinformatics methods to identify and characterize tomato defensins. Then, on the basis of sequence information, we selected a representative member of the family; we chemically synthesized a peptide (SolyC) corresponding * Correspondence to: Rosanna Capparelli, University of Naples ‘Federico II’, School of Biotechnological Sciences, Department of Soil, Plant, Environmental and Animal Production Sciences, Via Università 100, 80055 Portici, Naples, Italy. E-mail: capparel@unina.it a University of Naples ‘ Federico II’, School of Biotechnological Sciences, Department of Soil, Plant, Environmental and Animal Production Sciences, Via Università 100, 80055, Portici, Italy b University of Naples ‘Federico II’, School of Biotechnological Sciences, Department of Biological Sciences, Via Mezzocannone 16, 80134, Naples, Italy c CRA-ORT, Agricultural Research Council, Research Centre for Vegetable Crops, Via Cavalleggeri 25, 84098, Pontecagnano, SA, Italy d University of Naples ‘Federico II’, Department of Soil, Plant, Environmental and Animal Production Sciences, Via Università 100, 80055, Portici, Italy e Department of Food Inspection IZS ME, via Salute 2, 80055, Portici, Italy Abbreviations used: LPS, lipopolysaccharide; AMP, antimicrobial peptides; ASA, acetylsalicylic acid; MIC, minimum inhibitory concentration. J. Pept. Sci. 2012; 18: 755–762 Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd. Research Article Received: 25 July 2012 Revised: 3 October 2012 Accepted: 5 October 2012 Published online in Wiley Online Library: 4 November 2012 (wileyonlinelibrary.com) DOI 10.1002/psc.2462 755