Structural features of plant chitinases and chitin-binding proteins

Structural features of plant chitinases and chitin-binding proteins are discussed. Many of these proteins consist of multiple domains, of which the chitin-binding hevein domain is a predominant one. X-ray and NMR structures of representatives of the major classes of these proteins are available now, and are used to describe the structures of the other ones. Conserved positions of Cys residues can be taken as evidence for identically located disulfide bridges or cysteine residues. The current classification of chitinases is unsatisfactory and needs to be replaced by an evolutionarily more correct one. As the currently known three-dimensional structures of chitinases are those from barley and the rubber tree, Hevea brasiliensis, it is proposed to adopt the designation b-type (classes I, II and IV) and h-type (classes III and V) chitinases, respectively.     

LysM proteins in mammalian fungal pathogens

The LysM domain is a highly conserved carbohydrate-binding module that recognizes polysaccharides containing N-acetylglucosamine residues. LysM domains are found in a wide variety of extracellular proteins and receptors from viruses, bacteria, fungi, plants and animals. LysM proteins are also present in many species of mammalian fungal pathogens, although a limited number of studies have focused on the expression and determination of their putative roles in the infection process. This review summarizes the current knowledge and recent studies on LysM proteins in the main morphological groups of fungal pathogens that cause infections in humans and other mammals. Recent advances towards understanding the biological functions of LysM proteins in infections of mammalian hosts and their use as potential targets in antifungal strategies are also discussed.     

Evaluation of the antifungal activity of the purified chitinase 1 from the filamentous fungus Aphanocladium album

Abstract Crude protein preparations from the culture filtrate of the filamentous fungus Aphanocladium album , a hyperparasite of rust fungi, strongly inhibited growth of a strain of the fungus Nectria haematococca pathogenic on pea. Crude protein from the filtrate of the variant E3 of A. album , hyperproducing chitinase, was less inhibitory than crude protein from the filtrate of the wild-type strain E1. The antifungal potential of a purified chitinase from A. album , called chitinase 1, was compared to that of a plant chitinase with known antifungal activity, obtained from pea ( Pisum sativum ). Although purified chitinase 1 of A. album degraded chitin more completely than did pea chitinase, it did not inhibit growth of N. haematococca , either alone or in the presence of a pea β-1,3-glucanase. Furthermore, chitinase 1 from A. album failed to enhance the antifungal activity of pea chitinase. These results indicate that the extracellular proteins of A. album inhibit growth of some fungi by other means than through their chitinase 1 activity.     

The role of chitinase from Lecanicillium antillanum B-3 in parasitism to root-knot nematode Meloidogyne incognita eggs

B-3 fungal isolate was isolated from soil samples of Gwangju in Korea. Based on morphological and phylogenetic analysis, it was designated as Lecanicillium antillanum B-3 (syn. Verticillium antillanum B-3). The fungus was a chitinolytic-nematophagous microorganism. B-3 chitinase activity from 0.5% swollen chitin broth medium reached the highest level on the sixth day and then plateaued until 12 days. B-3 isolate showed the high rate of parasitism on Meloidogyne incognita eggs with more than 90% infection rate on the third day after treatment. B-3 crude chitinase damaged the eggshell structures more than 78% based on lactoglycerol staining data at a final protein concentration of 14.6 µg mL^?1 on the fourth day following treatment. Partially purified chitinase with molecular 37 kDa from DEAE-Sephadex chromatography also showed damaging effect on the eggs. These results suggested that chitinase from B-3 isolate was responsible for degradation of M. incognita eggshell structures.     

The molecular mechanism of stipe cell wall extension for mushroom stipe elongation growth

Stipe elongation growth is one of the remarkable characteristics of the growth and development of basidiomycete fruiting bodies. Stipe elongation is resulting from the lateral extension of stipe cells. The stipe cell is enclosed within a thin cell wall which must be loosened to expand the wall surface area for accommodation of the enlarged protoplast as the stipe cell elongates. In fungal cell walls, chitin molecules associate with each other by interchain hydrogen bonds to form chitin microfibrils which are cross-linked covalently to matrix polysaccharides. Early, some scientists proposed that stipe elongation was the result of enzymatic degradation of wall polysaccharides, whereas other researchers suggested that stipe elongation resulted from nonhydrolytic disruption of the hydrogen bonds by turgor pressure between wall polysaccharides. Recently, an extensometer was used to determine stipe wall extension for elucidation of the molecular mechanism of stipe elongation. In Coprinopsis cinerea, the native stipe cell wall is induced to extend by acidic buffers and the acid-induced native wall extension activity is located in the growing apical stipe region. A series of current experiments indicate that chitinases play a key role in the stipe wall extension, and β-glucanases mainly function in the wall remodeling for regulation of stipe wall expansibility to cooperate with chitinase to induce stipe wall extension. In addition, fungal expansin-like proteins can bind to chitin to enhance chitin hydrolysis, and their expression pattern is consistent with the stipe elongation growth, which is suggested to play an auxiliary role in the stipe wall extension.     

Substrate specificity of the β-1, 4-N-acetylglucosaminidases of vertebrates

A true chitinase, i.e. a poly-β-1, $\text{4-N-}\text{acetylglucosaminidase}$ specific of the hydrolosis of chitin and thus devoid of any lysozymic activity, has been localized in the gastric mucosa extracts and/or in the pancreas extracts of some vertebrate species (frog, lizard and mammals), the diet of which contains chitin. This observation confirms the relation existing between the feeding habits of vertebrates and the ability to synthesize specific chitinolytic enzymes. Furthermore, chitinolytic activity bound to lysozomic activity has been observed in the extracts of other organs such as the spleen of the carp and the kidneys of the dog, the rabbit and the ferret. In these cases, the chitinolytic activity seems to be due to the presence of lysozymes with different degrees of activity on the β-1, $\text{4-N-}\text{acetylglucosaminic}$ bounds of chitin.     

Enzymatic production of N-acetyl-D-glucosamine by solid state fermentation of chitinase by Penicillium ochrochloron MTCC 517 using agricultural residues

The optimization studies for production of chitinase were carried out by response surface methodology (RSM) based on statistics experimental design using three substrates, which were wheat, rice and red gram bran. 2⁴ full factorial central composite design was applied to evaluate optimal combinations of variables. These variables were chitin concentration, initial moisture content, inoculum level, and incubation time. The results of second order polynomial showed that all four variables had significant effect on chitinase production. Maximum chitinase activity was recorded for wheat bran (2443.23 U g⁻¹) than rice (1216.65 U g⁻¹) and red gram bran (961.32 U g⁻¹). An overall 3-fold increase in chitinase activity was achieved using optimized strategies of RSM. Growth of the fungus on all bran particles have been visualized by scanning electron microscopy. These results indicated the potential of Penicillium ochrochloron for economical production of chitinase using agricultural residues. TLC and HPLC analysis of colloidal chitin hydrolysate with partially purified chitinases revealed that the major reaction product was monomeric GlcNAc indicating the potential of these enzymes for efficient production of GlcNAc.