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BACKGROUND: Heterologous protein expression in microorganisms may contribute to identify and demonstrate antifungal activity of novel proteins. The Solanum nigrum osmotin-like protein (SnOLP) gene encodes a member of pathogenesis-related (PR) proteins, from the PR-5 sub-group, the last comprising several proteins with different functions, including antifungal activity. Based on deduced amino acid sequence of SnOLP, computer modeling produced a tertiary structure which is indicative of antifungal activity. RESULTS: To validate the potential antifungal activity of SnOLP, a hexahistidine-tagged mature SnOLP form was overexpressed in Escherichia coli M15 strain carried out by a pQE30 vector construction. The urea solubilized His6-tagged mature SnOLP protein was affinity-purified by immobilized-metal (Ni2+) affinity column chromatography. As SnOLP requires the correct formation of eight disulfide bonds, not correctly formed in bacterial cells, we adapted an in vitro method to refold the E. coli expressed SnOLP by using reduced:oxidized gluthatione redox buffer. This method generated biologically active conformations of the recombinant mature SnOLP, which exerted antifungal action towards plant pathogenic fungi (Fusarium solani f. sp.glycines, Colletotrichum spp., Macrophomina phaseolina) and oomycete (Phytophthora nicotiana var. parasitica) under in vitro conditions. CONCLUSION: Since SnOLP displays activity against economically important plant pathogenic fungi and oomycete, it represents a novel PR-5 protein with promising utility for biotechnological applications.

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beta-N-Acetylhexosaminidases (EC 3.2.1.52) belong to an enzyme family that hydrolyzes terminal beta-d-N-glucosamine and beta-d-N-galactosamine residues from oligosaccharides. In this report, we purified a novel beta-N-acetylhexosaminidase (Pcb-NAHA1) from the marine zoanthid Palythoa caribaeorum by applying ammonium sulfate fractionation, affinity chromatography on a chitin column, followed by two rounds of size exclusion chromatography. SDS-PAGE analysis indicated a single band protein of apparent homogeneity with a molecular mass of 25kDa. The purified enzyme preferentially hydrolyzed p-nitrophenyl-2-acetoamide-2-deoxyamide-2-deoxy-beta-d-N-acetylglucosamide (pNP-GlcNAc) and to a lesser extent p-nitrophenyl-2-acetoamide-2-deoxyamide-2-deoxy-beta-d-N-acetylgalactosamide (pNP-GalNAc). Detailed kinetic analysis using pNP-GlcNAc resulted in a specific activity of 57.9 U/mg, a K(m) value of 0.53 mM and a V(max) value of 88.1 micromol/h/mg and k(cat) value of 0.61s(-1). Furthermore, purified Pcb-NAHA1 enzyme activity was decreased by Hg Cl(2) or maltose and stimulated in the presence of Na(2)SeO(4,) BaCl(2), MgCl(2,) chondroitin 6-sulfate, and phenylmethylsulfonylfluoride. The optimum activity of Pcb-NAHA1 was observed at pH 5.0 and elevated temperatures (45-60 degrees C). Direct sequencing of proteolytic fragments generated from Pcb-NAHA1 revealed remarkable similarities to plant chitinases, which belong to family 18, although no chitinase activity was detected with Pcb-NAHA1. We conclude that beta-N-acetylhexosaminidases, representing a type of exochitinolytic activity, and endo-chitinases share common functional domains and/or may have evolved from a common ancestor.

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The Mexican bean weevil, Zabrotes subfasciatus, feeds on several seeds such as Vigna unguiculata, Phaseolus vulgaris, and Pisum sativum, causing severe crop losses. This ability to obtain essential compounds from different diets could possibly be explained due to a wide variability of digestive proteinases present in the weevil's midgut. These may improve digestion of many different dietary proteins. Coleopteran serine-like proteinases have not been thoroughly characterized at the molecular level. In this report, a full-length cDNA encoding a trypsin-like protein, named ZsTRYP, was isolated from Z. subfasciatus larvae using RT-PCR, 5' and 3' RACE techniques. The quantitative real-time PCR analysis strongly correlated the Zstryp transcript accumulation to the major feeding developmental larval stage. Zstryp cDNA was subcloned into pET101 vector and expressed in a Escherichia coli BL21(DE3) strain. Nickel-nitrilotriacetic acid (Ni-NTA) affinity chromatography was used to purify a 29.0-kDa recombinant enzyme. The purified ZsTRYP was then assayed with several synthetic peptide substrates and also challenged with different inhibitors. The biochemical data allowed us to classify ZsTRYP as a trypsin. Moreover, homology modeling analysis indicated a typical trypsin structural core and a conserved catalytic triad (His(41), Asp(86), and Ser(182)).

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Alpha-amylase inhibitors have important roles in plant defense mechanisms, particularly against insects, and several of these inhibitors have been expressed in different crops to increase their resistance to particular insects. In this work, we report the cloning and expression of a gene encoding for a new alpha-amylase inhibitor (BIII) from rye (Secale cereale) seeds. The BIII gene contains 354 nucleotides that encode for 118 amino acids sequence. A 313 bp fragment of the gene was expressed in Escherichia coli and resulted in a functional inhibitor that reduced the activity of alpha-amylases of larvae of the coleopteran pests Acanthoscelides obtectus, Zabrotess subfasciatus and Anthonomus grandis. In contrast, the inhibitor did not inhibit the activity of porcine pancreatic alpha-amylase. Although the amino acid sequence of BIII showed high identity with those of bifunctional inhibitors, the recombinant protein was unable to inhibit trypsin-like serine proteinases. The effects of recombinant BIII were evaluated in vivo against A. grandis. When first instar larvae were reared on an artificial diet containing four different concentrations of BIII, a reduction in larval weight and a mortality of 83% were observed at the highest concentration.

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The cotton boll weevil, Anthonomus grandis, is an economically important pest of cotton in tropical and subtropical areas of several countries in the Americas, causing severe losses due to their damage in cotton floral buds. Enzymatic assays using gut extracts from larval and adult boll weevil have demonstrated the presence of digestive serine proteinase-like activities. Furthermore, in vitro assays showed that soybean Kunitz trypsin inhibitor (SKTI) was able to inhibit these enzymes. Previously, in vivo effects of black-eyed pea trypsin chymotrypsin inhibitor (BTCI) have been demonstrated towards the boll weevil pest. Here, when neonate larvae were reared on an artificial diet containing SKTI at three different concentrations, a reduction of larval weight of up to 64% was observed for highest SKTI concentration 500 microM. The presence of SKTI caused an increase in mortality and severe deformities of larvae, pupae and adult insects. This work therefore represents the first observation of a Kunitz trypsin inhibitor active in vivo and in vitro against A. grandis. Bioassays suggested that SKTI could be used as a tool in engineering crop plants, which might exhibit increased resistance against cotton boll weevil.

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