Peptides in plants

Several examples of production of antimicrobial peptides in plants have been reported, but these are predominantly from the perspective of protecting the plant against microbial insult, rather than use of the plant as a biofactory for the large-scale production of peptide. 

The number of reports suggesting that peptides in plants play an important role as hormone-like molecules has been increasing in recent years. Most of the biologically active peptides are biosynthesized from precursors by processing and/or specific modification, as was the case with PSK and CLE peptides. In order to develop peptide hormone research, it is necessary to accurately determine the chemical structures of mature peptides. Once the chemical structures of the peptides are determined, it is expected that research will further expand, focusing on biosynthesis, receptors, and signal transduction. 

Steffens, J.C., 1990. The heavy metal binding peptides in plants. Ann. Rev. Plant Physiol. Plant Mol. Biol. 41, 553-575. 

Saska, L, Colgrave, M.L., Jones, A.etal. (2008) Quantitative analysis of backbone-cycUsed peptides in plants. Journal... 

Nicotinic acid is found in plants associated with both peptides and polysaccharides. For example in wheat bran, two forms are described a peptide with a molecular weight of approximately 12,000 and a carbohydrate complex that is called niacytin. Polysaccharides isolated from wheat bran have been found to contain 1.05% nicotinic acid in bound form. Hydrolysis yielded a fragment identified as P-3-O-nicotinoyl-D-glucose (25). 

Although carotenogenesis in plants takes place in plastids, all of the carotenoid biosynthesis genes are nuclear encoded and their polypeptide products are imported into the plastids. Therefore, they contain a N-terminal transit peptide sequence. For example, the size of the transit peptide of PSY from ripe tomato fruit is approximately 9 kDa, corresponding to about 80 amino acid residues (Misawa et al, 1994). 

Esterification increases the lipophilic character of the pigments that has been recogiuzed as an important factor for interactions with the peptide chains of proteins. The hydrolysis of this side chain results in chlorophyllides and the concomitant removal of the Mg + ion in pheophorbides. Only a Umited number of natural chlorophylls in plants and photosynthetic organisms has been described and is well... 

Some divalent cations such as Cu and Pb form very stable complexes with pectate, but are unlikely to be present at sufiScient concentration in the apoplast of plants to form a major fraction of the counterions associated with the pectic fraction in vivo. The Al ion may deserve closer examination, as it is certainly able to displace Ca from cell walls and reaches substantial concentrations in plant roots under some conditions [60,61]. aluminium is not usually considered to be freely translocated, however. Basic peptides with their negative charges spaced at a similar interval to galacturonans (0.43 nm or a small multiple thereof) can in principle have a very high afiBnity for pectate [62,63], but the extensins that are associated with the most insoluble pectic fractions [M] do not appear to have this type of structure. The possibility that the non-extractable pectic polymers in most cell walls are very strongly complexed with some cation other than Ca " cannot be ruled out, but there is little evidence to support it at present. 

W. N. Fischer. B. Andre, D. Rentsch, S. Krolkiewicz, M. Tegeder, K. Breitkreuz, and W. B. Frommer, Amino acid transport in plants. Trends Plant Sci. 3 188 (1998), H. Y. Steiner, W. Song, L. Zhang, F. Naider, J. M. Becker, and G. Stacey, An Arahidopsis peptide transporter is a member of a novel family of membrane transport proteins. Plant Cell 6 189 (1994). 

Polar organic compounds such as amino acids normally do not polymerize in water because of dipole-dipole interactions. However, polymerization of amino acids to peptides may occur on clay surfaces. For example, Degens and Metheja51 found kaolinite to serve as a catalyst for the polymerization of amino acids to peptides. In natural systems, Cu2+ is not very likely to exist in significant concentrations. However, Fe3+ may be present in the deep-well environment in sufficient amounts to enhance the adsorption of phenol, benzene, and related aromatics. Wastes from resinmanufacturing facilities, food-processing plants, pharmaceutical plants, and other types of chemical plants occasionally contain resin-like materials that may polymerize to form solids at deep-well-injection pressures and temperatures. 

The seeds and vegetative part of plants contain several sorts of inhibitors of insect, fungal, mammalian, and endogenous proteinases. These inhibitors may be involved in plant defense mechanisms against predators and participate in the development of the plant itself. Peptidic proteinase inhibitors are well studied in the families Fabaceae, Poaceae, Asteraceae, and Solanaceae (37). Non-proteinaceous inhibitors of serine... 

Ferritins have been found in a wide range of species, and sequence data - some, as in the first ever sequence of horse spleen apoferritin (Heusterspreute and Crichton, 1981) determined by direct methods, but many now by DNa sequencing 1, have been deposited for more than 70 ferritins. They vary in length from 154-185 residues per subunit. Some ferritins have N-terminal extensions which lie on the outside of the assembled shell and target the ferritin to a specific destination such as plastids in plants and yolk sac in snails (Andrews etah, 1992 Lobreaux etah, 1992). For example, pea ferritin is synthesized with an N-terminal extension of 75 residues, which is missing from the mature protein. The first part of this extension is a chloroplast-targetting sequence of 47 residues, which is lost on entry into the plastid. The second part, an extension peptide, is lost prior to assembly of the... 

While many sulfur-containing fungal secondary metabolites are known, they are found less frequently than in plants. There is a structural range from CH2S6, 1,2,3,4,5,6-hexathiapane, from Lentinus edodes, to C82Hii4N2oOi7S, a 13-unit peptide containing methionine from Saccharomyces cerevesiae,13... 

All entries of Table 2.1 belong to samples representing the animal kingdom. In order to demonstrate the generality of peptidome concept we analyzed the extract of Avenasativa oat acrospires [34]. Table 2.2 provides the list of peptides found in that plant as well as their tentative protein precursors. Peptide formation in this case seems somewhat less intensive and on the average the peptides are longer than in animal samples. We consider this result as a proof of peptidome formation in plants. Still peptidomics of plants is apparently in its embryonic state and more results are expected in the near future. Procaryotes are not yet studied for generation of peptide pools. 

The three-dimensional structural architecture of plant defensins is exemplified by the structure of Rs-AFP, ° which comprises an N-terminal /3-strand followed by an ct-helix and two /3-strands (/3a/3/3 configuration). The /3-strands form a triple-stranded antiparallel /3-sheet. The three-dimensional structure is stabilized by three disulfide bonds. In general, in plant defensins two disulfide bonds form between the ct-helix and the central /3-strand. A third disulfide bond stabilizes the structure by linking the /3-strand after the helix to the coiled part after the ct-helix. This motif is called the cysteine-stabilized a/3-motif (CSa/3)" and also occurs in toxins isolated from insects, spiders, and scorpions.The fourth disulfide bond links the C-terminal end of the peptide with the N-terminal /3-strand. Two plant defensins, PhDl and PhD2, feature a fifth disulfide bond and have been proposed to be the prototypes of a new subclass within plant defensins." As a result of these structural features the global structure of plant defensins is notably different from o //3-thionins, which is one of the reasons for the different nomenclature. The structures of plant defensins Rs-AFP ° and NaDf are shown in Figure 6, where they are compared to the thionin /3-purothionin and the structurally more related drosomycin and charybdotoxin. ... 

Another interesting activity of plant defensins has been described by Kushmerick et al. for two defensins called 7I- and 72-zeathionin from Zea mays. These two peptides showed fast and reversible inhibition of sodium channels in rat tumor cell lines. Owing to an overall conservation of ion channels in eukaryotic cells it is feasible to assume that sodium channels in plant pests may be targets for these plant defensins, although their activities have not been determined in vivo. ... 

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