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We have demonstrated that wheatwin1, a wheat pathogenesis-related protein of class 4 (PR4), has ribonuclease activity. Both native and recombinant proteins hydrolyse RNA from wheat coleoptils and have antifungal activity. Sepharosebound wheatwin1 is able to interact with either wheat or Fusarium culmorum RNA. 3D modelling studies showed that, like ribonucleases A and T1, the action mechanism should involve two His residues, an Arg residue and an Asp residue.

The white-rot fungus Trametes trogii excretes a main laccase showing a molecular mass of 70 kDa, acidic isoelectric point and N-terminal sequence homologous to that of several phenol oxidases. The purified enzyme oxidizes a number of phenolic and non-phenolic compounds; recalcitrant molecules may be converted into substrates by introducing, in the correct position, o- or p-orienting ring-activating groups.

We conclude that catestatin is cleaved extensively in vivo, and the peptide is released by exocytosis. In chromaffin granules, the major form of catestatin is cleaved at dibasic sites, while smaller carboxyl-terminal forms also occur. Knowledge of cleavage sites of catestatin from chromogranin A may provide a useful starting point in analysis of the relationship between structure and function for this peptide.Chromogranin A, the major soluble protein in catecholamine storage vesicles, not only stabilizes the core of such vesicles (1) but also serves as a prohormone cleaved into several biologically active peptides, including the insulin release-inhibitory fragments pancreastatin (2) and ␤-granin (3-5), the vasodilator vasostatin (6, 7), and the parathyroid hormone release-inhibitory parastatin (8). Recently we described an additional chromogranin A fragment, catestatin (bovine chromogranin A 344 -364), which acts specifically as a potent (IC 50 ϳ200 -400 nM) nicotinic cholinergic antagonist to inhibit catecholamine release (9, 10), suggesting a novel autocrine feedback mechanism controlling sympathochromaffin exocytosis. Initial studies of catestatin relied on synthetic peptides (10); hence, the existence of the peptide in vivo remains unexplored, as do its precise cleavage sites from chromogranin A.In this study, we explored processing of the catestatin region of chromogranin A in secretory granules of chromaffin cells and sympathetic nerves, as well as in human pheochromocytomas. We documented catestatin cleavage from chromogranin A and determined the precise endogenous cleavage sites bounding catestatin in bovine and human chromaffin granules by chromatographic separations coupled with amino-terminal amino acid sequencing, immunoprecipitation, and matrix-assisted laser desorption ionization (MALDI) 1 mass spectrometry. We confirmed catestatin's regulated secretion by chromaffin cells. A major form of catestatin was processed at dibasic sites (bovine chromogranin A 332-364 or human chromogranin A 340 -372 ), while a smaller form was also identified (bovine chromogranin A 343-362 ). Both larger and smaller size forms were synthesized; each displayed specific antagonism of nicotinic cholinergicstimulated catecholamine release, while the smaller form had greater potency of inhibition. MATERIALS AND METHODS Preparation of TissueFractions-All preparative steps on tissues or protein fractions were conducted at 0 -4°C. Bovine adrenal medullary chromaffin granules were prepared by centrifugation on 0.3 M/1.6 M sucrose density step gradients, as described previously (10). After granule hypotonic lysis and centrifugal removal of granule membranes, the soluble proteins and peptides in the supernatant were size-fractionated on a 2.6 ϫ 80-cm Sephacryl S-300 column (Amersham Pharmacia Biotech), eluting with the volatile buffer 0.3 M ammonium acetate, pH 6.5, as described previously (11). The buffer was removed by lyophilization before further studies. In some experiments, bovine chromaffin granule proteins/peptides (200 l c...

a b s t r a c t PR4 proteins possess antifungal activity against several pathogenic fungi suggesting a pivotal role in defence reactions against plant pathogen attack. We already showed that wheatwin1, a wheat PR protein of class 4, is endowed with ribonuclease activity. In this study we produced three mutants altering the active site and performed comparative analysis with the native protein also in the presence of the ribonuclease inhibitor 5 0 -ADP. We characterized the RNA binding site and its interaction with 5 0 -ADP by 3D modelling and docking studies. Moreover, in vitro antifungal assays have been carried out in order to study the relationship between antifungal and ribonuclease activities. Finally, localization of wheatwin1 in Fusarium culmorum spores was evaluated using fluorescence light microscope.

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We have purified and characterized a protein from the water-soluble fraction of wheat kernel (Triticum aestivum cv. S. Pastore) consisting of a single polypeptide chain blocked at its N-terminus by a pyroglutamate residue; the complete amino acid sequence has been determined by automated sequence analysis performed on peptide fragments obtained by enzymatic hydrolyses of the protein. Homology studies have shown that this protein is very similar (97% sequence identity) to the previously characterized wheatwin1 as well as to other members of the pathogenesis-related (PR) proteins of class 4; in analogy with wheatwin1, we have termed this protein wheatwin2. Both wheatwin1 and wheatwin2 have specific antifugal activity toward the wide-host-range pathogen Botrytis cinerea and the wheat-specific pathogenic fungi of wheat Fusarium culmorum and Fusarium graminearum of groups 1 and 2. On the basis of their structural and functional properties, wheatwin1 and wheatwin2 can be classified as members of the PR4 protein family; this represents the first report concerning the presence of this kind of protein in wheat.