Chitin

About: Chitin is a research topic. Over the lifetime, 6590 publications have been published within this topic receiving 253993 citations.

Characterization of a novel, antifungal, chitin-binding protein from Streptomyces tendae Tü901 that interferes with growth polarity.

Abstract: Proteins with antifungal activity have been isolated from plants, insects, and fungi and characterized. Plant antifungal proteins, including the cysteine-rich small defensins, ribosome-inactivating proteins, lipid transfer proteins, polygalacturonase inhibitor proteins, nonenzymatic chitin-binding proteins, and pathogenesis-related (PR) proteins, appear to comprise defense mechanisms against fungal attack (54). Many of these proteins are rapidly induced upon infection with fungal, bacterial, viral, or viroidal pathogens or by related forms of stress. Among the induced proteins are the PR proteins, which have been classified into families based on amino acid sequence similarities, serological properties, and function (22, 24, 43). Members of the five major families (1 to 5) have been shown to have in vitro antifungal activities. PR proteins of families 2 and 3 (PR-2 and PR-3 proteins) include β-1,3-glucanases and chitinases, respectively, which act synergistically in degrading fungal cell walls and inhibit growth of fungi. Many of the PR-4 proteins have nonenzymatic chitin-binding activity, and PR-5 proteins are related to salt-induced osmotins, which have been shown to permeabilize the fungal plasma membrane and inhibit spore germination and hyphal growth (1, 47, 51). A small histidine-rich antifungal protein and cysteine-rich antifungal proteins have been isolated from insects (8, 20). The latter proteins, which have significant sequence similarity to the 5-kDa plant defensins, inhibit spore germination and cause partial lysis of fungal hyphae. Small, highly basic, and cysteine-rich antifungal proteins not related to plant antifungal proteins have been purified from the extracellular medium of some imperfect ascomycetes (25, 31). These proteins reveal some sequence similarity to phospholipase A2, but their molecular mode of action is not known. Antifungal proteins are of great biotechnological interest because of their potential use as food and seed preservative agents and for engineering plants for resistance to phytopathogenic fungi (6). Various studies have revealed that transgenic plants overexpressing genes of the PR-1, PR-2, PR-3, and PR-5 families mediate host plant resistance to phytopathogenic fungi, and coexpression of multiple antifungal protein genes in transgenic plants seems to be more effective than expression of single genes (for a review, see reference 54). Antifungal proteins have not yet been isolated from streptomycetes and other bacteria. Streptomycetes are gram-positive, mycelium-forming soil bacteria that have the capacity to produce a great variety of secreted proteins, including hydrolytic enzymes that degrade organic material in the soil, such as chitin, cellulose, xylan, and starch (33), and enzyme inhibitors (7, 14, 30). Furthermore, streptomycetes have the exceptional ability to produce a broad range of low-molecular-weight antibiotics and other secondary metabolites; many of these compounds have antibacterial and antifungal properties and are used as agents in medicine and agriculture. Streptomyces tendae Tu901 produces antibiotics of various chemical structures, including cyclohexenylglycine, an isoleucine antagonist with antibacterial activity (23); the naphthoquinone compound juglomycin, which has antitumor activity (11); and chlorothricin, a glycosylated macrolide antibiotic that acts as an antagonist of acetyl-coenzyme A in bacteria (9). In addition, the strain synthesizes various nikkomycins, which are peptidyl nucleoside antibiotics. Nikkomycins act as specific inhibitors of chitin synthetases and have high antifungal, insecticidal, and acaricidal activity (for a review, see reference 12). In an attempt to isolate nikkomycin biosynthesis genes, we transformed a nikkomycin-nonproducing mutant of S. tendae Tu901 with DNA fragments from S. tendae Tu901 cloned into the multicopy plasmid pIJ699 and screened for antifungally active transformants, using Paecilomyces variotii as the test organism. In the course of these experiments, we cloned a gene for a protein that exhibits antifungal activity. Here, we present the characterization of this antifungal protein, AFP1, and its gene and show that AFP1 is a chitin-binding protein that strongly binds to the cell wall of germinated conidia and to hyphal tips of sensitive fungi and interferes with their growth polarity.

Carbon source control on β-glucanases, chitobiase and chitinase from Trichoderma harzianum

Abstract: The cell-wall degrading enzymes β-glucanase and chitinase have been suggested to be essential for the mycoparasitic action of Trichoderma species against plant fungal pathogens. For this reason, the production in different carbon sources of extracellular β-1,3-glucanase, β-1,6-glucanase, chitobiase and chitinase was studied in a mycoparasitic strain of Trichoderma harzianum. Maximal β-glucanase specific activities were detected in media supplemented with either pustulan (β-1,6-glucan), nigeran (α-1,3-glucan alternating with α-1,4-glucan), chitin or Saccharomyces cerevisiae or Botrytis cinerea purified cell walls, whereas the highest chitinase specific activity was obtained in medium supplemented with chitin. Furthermore, β-glucanase, chitobiase and chitinase activities showed an increase parallel to increasing concentrations of either pustulan or chitin added to the cultures, although the extent of this increase varied with the different enzymes. The culture filtrates of T. harzianum grown in these carbon sources also showed lytic activity on purified cell walls of S. cerevisiae and B. cinerea. The enzyme synthesis seemed to be repressed by glucose, 8-hydroxyquinoline, which inhibits transcription, or cycloheximide, an inhibitor of protein synthesis.