Plant antimicrobial peptides (AMPs) have evolved differently from AMPs from other life forms. They are generally rich in cysteine residues which form multiple disulfides. In turn, the disulfides cross-braced plant AMPs as cystine-rich peptides to confer them with extraordinary high chemical, thermal and proteolytic stability. The cystine-rich or commonly known as cysteine-rich peptides (CRPs) of plant AMPs are classified into families based on their sequence similarity, cysteine motifs that determine their distinctive disulfide bond patterns and tertiary structure fold. Cystine-rich plant AMP families include thionins, defensins, hevein-like peptides, knottin-type peptides (linear and cyclic), lipid transfer proteins, α-hairpinin and snakins family. In addition, there are AMPs which are rich in other amino acids. The ability of plant AMPs to organize into specific families with conserved structural folds that enable sequence variation of non-Cys residues encased in the same scaffold within a particular family to play multiple functions. Furthermore, the ability of plant AMPs to tolerate hypervariable sequences using a conserved scaffold provides diversity to recognize different targets by varying the sequence of the non-cysteine residues. These properties bode well for developing plant AMPs as potential therapeutics and for protection of crops through transgenic methods. This review provides an overview of the major families of plant AMPs, including their structures, functions, and putative mechanisms.

Antimicrobial Peptides from Plants

The functions of a number of amino acid residues in proteins have been studied by chemical modification techniques and much useful information has been obtained. Methods using dicarbonyl compounds for the modification of arginine residues are the most recent to have been developed. Since their introduction about 10 years ago, they have led to the identification of a large number of enzymes and other proteins that contain arginine residues critical to biological function. These reagents are discussed in terms of their chemical reactivity and mechanisms of action and in relation to the unique chemical properties of the guanidinium group. Butanedione, phenylglyoxal and cyclohexanedione are the most commonly employed arginyl reagents, and their relative advantages are examined. A survey of the functional role of arginine residues in enzymes and other proteins is presented in which nearly 100 examples are cited. The prediction that arginine residues would be found to serve a general role as anionic binding sites in protein has obviously been validated. The genetic and physiological implications of the selection of arginine for this important function are discussed.

Arginyl residues and anion binding sites in proteins.

The increasing threat of antibiotic resistance in pathogenic bacteria and the dwindling supply of antibiotics available to combat these infections poses a significant threat to human health throughout the world. Antimicrobial peptides (AMPs) have long been touted as the next generation of antibiotics capable of filling the anti-infective void. Unfortunately, peptide-based antibiotics have yet to realize their potential as novel pharmaceuticals, in spite of the immense number of known AMP sequences and our improved understanding of their antibacterial mechanism of action. Recently, the immunomodulatory properties of certain AMPs have become appreciated. The ability of small synthetic peptides to protect against infection in vivo has demonstrated that modulation of the innate immune response is an effective strategy to further develop peptides as novel anti-infectives. This review focuses on the screening methods that have been used to assess novel peptide sequences for their antibacterial and immunomodulatory properties. It will also examine how we have progressed in our ability to identify and optimize peptides with desired biological characteristics and enhanced therapeutic potential. In addition, the current challenges to the development of peptides as anti-infectives are examined and the strategies being used to overcome these issues are discussed.

Peptide design for antimicrobial and immunomodulatory applications

Activity of extracts from wild edible herbs against postharvest fungal diseases of fruit and vegetables

(e ) Structural and evolutionary relationships of prolamins (f) What are prolamins? . . . . . . . ( 2 ) The zS albumins . . . . . . . . (a) Distribution and properties . . . . . (b) Evolutionary relationships . (c) Biological activity . . . . . . . ( d ) Use in genetic engineering (3) Globulins . . . . . . . . . (a) I IS globulins . . . . . . . . (b) 7 s globulins . . . . . . . . (c) Are 7 s and I IS globulins related? . . . . (d) Cereal globulins . . . . . . . (4) Synthesis and deposition . . . . . . . (a ) Protein folding and assembly in the ER . . . (b) Protein targeting and protein body formation . . ( 5 ) Comparative properties of seed storage proteins . . (a) Solubility . . . . . . . . . (b) Amino acid composition and protein structure . . (c) Subunit structures . . . . . . . (d) Polymorphism and post-translational processing . I11 . Seed storage proteins of Gymnosperms . . . . . IV . Tuber storage proteins . . . . . . . . ( I ) Potato . . . . . . . . . . ( 7 ) Sweet potato . . . . . . . . . (3) Taro . . . . . . . . . . (4) Yams . . . . . . . . . . ( 5 ) General features of tuber storage proteins . . . . . . . . ( I ) Soybean VSPs . . . . . . . . . ( 2 ) VSPs in deciduous trees . . . . . . . . . . . . . . . ( I ) Bryophytes . . . . . . . . . ( 2 ) Pteridophytes . . . . . . . . . (b) The prolamins of oats . . . . . .

Plant Storage Proteins

Antimicrobial peptides (AMPs), named lycocitin 1, 2 and 3, and a peptide with a monoisotopic molecular mass of 3038.70 Da were detected in the venom glands of the wolf spider Lycosa singoriensis .T wo of the peptides, lycocitin 1 and 2, are new AMPs whereas lycocitin 3 is highly homologous to lycotoxin II isolated from the venom of spider Lycosa carolinensis. In addition, two other peptides with monoisotopic masses of 2034.20 and 2340.28 Da showing the motif typical for antimicrobial peptides were also identified. These peptides and lycocitin 1, 2 and 3 were de novo sequenced using electron capture dissociation and low-energy collisional tandem mass spectrometry. The amino acid sequence of lycocitin 1 was determined as GKLQAFLAKMKEIAAQTL-NH2. Lycocitin 2 differs from lycocitin 1 by a replacement of a lysine residue for an arginine residue at the second position. Lycocitin 3 differs from the known lycotoxin II consisting of 27 amino acid residues by a deletion of Gly-26. Both lycocitin 1 and 2 inhibit growth of Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli )b acteria and fungi (Candida albicans, Pseudomonas aeruginosa) at micromolar concentrations. Copyright  2004 John Wiley & Sons, Ltd.

De novo sequencing of antimicrobial peptides isolated from the venom glands of the wolf spider Lycosa singoriensis.

Discovery of novel antimicrobial peptides with unusual cysteine motifs in dandelion Taraxacum officinale Wigg. flowers.

In this work, we isolated and characterized novel antifungal proteins from seeds of dandelion (Taraxacum officinale Wigg.). We showed that they are represented by five isoforms, each consisting of two disulphide-bonded large and small subunits. One of them, To-A1 was studied in detail, including N-terminal amino acid sequencing of both subunits, and shown to display sequence homology with the sunflower 2S albumin. Using different assays we demonstrated that dandelion 2S albumins possess inhibitory activity against phytopathogenic fungi and the oomycete Phytophtora infestans at micromolar concentrations with various isoforms differing in their antifungal activity. Thus, 2S albumins of dandelion seeds represent a novel example of storage proteins with defense functions.

Antifungal Activity of Storage 2S Albumins from Seeds of the Invasive Weed Dandelion Taraxacum officinale Wigg.

Antimicrobial peptides (AMPs) are natural antibiotics produced by all living organisms to combat pathogens. They are important effector molecules of the immune system both in animals and plants. AMPs are diverse in structure and mode of action. Based on homology of amino acid sequences and 3D structures several AMP families have been distinguished. They are defensins, thionins, lipid transfer proteins, hevein- and knottin-like peptides, and cyclotides. AMPs display broad-spectrum antimicrobial activity and thus show promise for the development of disease- resistant crops by genetic engineering and for the production of new-generation drugs. In this paper, the properties of the main AMP families (defensins and hevein-like peptides) and of a new 4-Cys plant AMP family are reviewed.

Ts. A. Egorov

Papers

De novo sequencing of antimicrobial peptides isolated from the venom glands of the wolf spider Lycosa singoriensis.

Discovery of novel antimicrobial peptides with unusual cysteine motifs in dandelion Taraxacum officinale Wigg. flowers.

Antifungal Activity of Storage 2S Albumins from Seeds of the Invasive Weed Dandelion Taraxacum officinale Wigg.

Defense peptides of plant immune system

Defense peptides from barnyard grass (Echinochloa crusgalli L.) seeds.