Chitinase

About: Chitinase is a research topic. Over the lifetime, 4690 publications have been published within this topic receiving 161786 citations. The topic is also known as: 1,4-beta-poly-N-acetylglucosaminidase & poly-beta-glucosaminidase.

Primary structure and expression of mRNAs encoding basic chitinase and 1,3-beta-glucanase in potato.

Abstract: Infection of potato leaves (Solanum tuberosum L. cv. Datura) by the late blight fungus Phytophthora infestans, or treatment with fungal elicitor leads to a strong increase in chitinase and 1,3-beta-glucanase activities. Both enzymes have been implicated in the plant's defence against potential pathogens. In an effort to characterize the corresponding genes, we isolated complementary DNAs encoding the basic forms (class I) of both chitinase and 1,3-beta-glucanase, which are the most abundant isoforms in infected leaves. Sequence analysis revealed that at least four genes each are expressed in elicitor-treated leaves. The structural features of the potato chitinases include a hydrophobic signal peptide at the N-terminus, a hevein domain which is characteristic of class I chitinases, a proline- and glycine-rich linker region which varies among all potato chitinases, a catalytic domain, and a C-terminal extension. The potato 1,3-beta-glucanases also contain a N-terminal hydrophobic signal peptide and a C-terminal extension, the latter comprising a potential glycosylation site. RNA blot hybridization experiments showed that basic chitinase and 1,3-beta-glucanase are strongly and coordinately induced in leaves in response to infection, elicitor treatment, ethylene treatment, or wounding. In addition to their activation by stress, both types of genes are regulated by endogenous factors in a developmental and organ-specific manner. Appreciable amounts of chitinase and 1,3-beta-glucanase mRNAs were found in old leaves, stems, and roots, as well as in sepals of healthy, untreated plants, whereas tubers, root tips, and all other flower organs (petals, stamen, carpels) contained very low levels of both mRNAs. In young leaves and stems, chitinase and 1,3-beta-glucanase were differentially expressed. While chitinase mRNA was abundant in these parts of the plant, 1,3-beta-glucanase mRNA was absent. DNA blot analysis indicated that in potato, chitinase and 1,3-beta-glucanase are encoded by gene families of considerable complexity.

Characterization of an Exo-β-d-Glucosaminidase Involved in a Novel Chitinolytic Pathway from the Hyperthermophilic Archaeon Thermococcus kodakaraensis KOD1

Abstract: Chitin, an insoluble β-1,4-linked linear polymer of N-acetylglucosamine (GlcNAc), is the second most abundant organic compound on our planet after cellulose. Previously known biodegradation pathways of chitin are summarized in Fig. ​Fig.1A.1A. It is degraded into dimer units of GlcNAc (GlcNAc2) by the combination of endo- and exo-type chitinases (reactions 1 and 2). β-N-Acetylglucosaminidase (GlcNAcase; reaction 3) further hydrolyzes the dimer to form GlcNAc or releases GlcNAc from chitooligosaccharides (6). Some organisms degrade GlcNAc2 to GlcNAc and GlcNAc-1-phosphate by GlcNAc2 phosphorylase (reaction 4) (28) or convert the dimer to GlcNAc-6-phosphate-GlcNAc by a GlcNAc2 phosphotransferase system (reaction 5) followed by degradation to GlcNAc and GlcNAc-6-phosphate by 6-phospho-β-glucosaminidase (reaction 6) (15, 16). Another pathway for chitin degradation is proposed to occur through deacetylation of chitin by chitin deacetylase (reaction 7). The resulting deacetylated chitin, chitosan, is then degraded to glucosamine (GlcN) by chitosanase (endo-type enzyme [reaction 8]) in cooperation with exo-β-d-glucosaminidase (GlcNase; reaction 9) (6). In contrast to the many studies on chitinases, chitosanases, GlcNAcases, and chitin deacetylases, information concerning GlcNase has been quite limited (20, 22, 25, 36). Moreover, a gene encoding GlcNase has not yet been cloned from any source. FIG. 1. (A) Previously known chitin catabolic pathways from chitin to monosaccharides. Enzymes are displayed as 1, endochitinase; 2, exochitinase; 3, GlcNAcase; 4, GlcNAc2 phosphorylase; 5, GlcNAc2 phosphotransferase system; 6, 6-phospho-β-d-glucosaminidase; ... We previously reported the first cloning and characterization of chitinase from an archaeon (32, 33). The chitinase from the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1 (previously reported as Pyrococcus kodakaraensis KOD1) possesses endo- and exo-type catalytic domains together with three chitin-binding domains on a single polypeptide. It has also been clarified that this chitinase (ChiATk) produces GlcNAc2 as an end product from chitin. However, the fate of GlcNAc2 in T. kodakaraensis remained to be solved. Interestingly, no gene homologous to any of the known GlcNAc2-processing enzymes (GlcNAcase, GlcNAc2 phosphorylase, and GlcNAc2 phosphotransferase system) could be identified in the preliminary complete genome sequence of strain KOD1. This is also the case for other archaeal genomes, including those of Pyrococcus furiosus and Halobacterium sp. strain NRC-1, both of which possess putative chitinase genes (3, 24). These facts suggested the existence of a novel type of enzyme or an unknown chitinolytic pathway in Archaea. This study aimed to identify the enzymes involved in the downstream steps of chitinolysis after chitinase in T. kodakaraensis KOD1. Through a search of the T. kodakaraensis genome, we found a gene initially identified as a putative β-glycosyl hydrolase located near the chitinase gene and demonstrated that the gene product was a GlcNase. As a GlcNase gene has not yet been identified from any organism, including Archaea, we report the characterization of this GlcNase (GlmATk) and contemplate its contribution to a novel GlcNAc2 degradation pathway in the archaeon T. kodakaraensis (Fig. ​(Fig.1B1B).

Mutation analysis of the C-terminal vacuolar targeting peptide of tobacco chitinase: low specificity of the sorting system, and gradual transition between intracellular retention and secretion into the extracellular space.

Abstract: The C-terminal propeptide of tobacco (Nicotiana tabacum) chitinase A has been shown to be necessary and sufficient for targeting of chitinases to the plant vacuole. The sequence specificity of this vacuolar targeting peptide (VTP) has now been analysed using transient expression of chitinases in Nicotiana plumbaginifolia protoplasts. An extracellular cucumber chitinase, previously used as a secreted reporter protein in transgenic tobacco, was also secreted into the incubation medium by the transiently transformed protoplasts. Addition of six to seven amino acids at the C-terminus to generate the VTP of tobacco chitinase A were sufficient to cause retention of most of the cucumber chitinase within the protoplasts. The chitinase A itself, as well as a mutant lacking the N-terminal chitin-binding domain, were retained to 80% in the protoplasts when low concentrations of the plasmid were used in the transient expression system. At high concentrations of plasmid, causing high levels of transiently expressed chitinase, retention was reduced, indicating saturation of the sorting system. Deletion of the C-terminal methionine did not affect the intracellular location, but deletion of even a single internal amino acid of the VTP caused predominantly secretion of tobacco chitinase A. In contrast, exchanges of amino acids in the VTP as well as substitution of the VTP with random sequences had intermediary effects that covered the whole range from retention to secretion. The results suggest that the sorting system responsible for the diversion of secretory proteins to the vacuole has a low specificity for the sequence of C-terminal targeting peptides, and that sequence changes in the VTP allow a gradual transition from vacuolar retention to secretion.

Enhanced Resistance against a Fungal Pathogen Sphaerotheca humuli in Transgenic Strawberry Expressing a Rice Chitinase Gene

Abstract: Fragaria×Ananassa Duch. cv. Toyonoka is a main variety of strawberry in Japan, but it is susceptible to a pathogenic fungus, Sphaerotheca humuli. Rice chitinase gene under the control of cauliflower mosaic virus (CaMV) 35S promoter was introduced into the strawberry plants using Agrobacterium tumefaciens. The transgenic plants showed an increased resistance to the powdery mildew, S. humuli.