Genetics and molecular biology of chitin synthesis in fungi.

Thus, a greatly enhanced apparent chitin synthase activity is observed in membranes from an arthropod species when simultaneous degradation of chitin is inhibited.

Chitin biosynthesis as a target for antifungals, pp.

Jewess, P. J. 2003. Chitin Biosynthesis Inhibitors. Encyclopedia of Agrochemicals. .

The Danger of Chitin Synthesis Inhibitors - …

Nonomura and Ohara (1969) used pre-treatment such as dry heating, specialized growth media and long incubation times to isolate new species of Actinomadura, Microbispora, Micro tetraspora, Streptosporangium, Thermom- onospora and Thermoactinomyces. Many antibiotics are tested against a range of actinomycetes, bacteria and fungi representing types found in soil. From these, nystatin (50 mg/ml), acetidione (50 mg/ml), polymyxin B sulphate (5 mg/ml) and sodium penicillin (1 mg/ml) are generally selected for incorporation into a starch casein medium to achieve selective growth of actinomycetes on soil dilution plates.

to act as a chitin synthesis inhibitor

It was established that the final intermediate of chitin biosynthesis (UDP-N-acetylglucosamine) was formed in the isolated integuments in the presence of diflubenzuron and polyoxin-D.

the benzoylurea insecticide mode of action on chitin biosynthesis

Key enzymes The biosynthetic pathway of chitin can be thought of as consisting of three subreactions. The first set leads to the formation of the amino sugar, GlcNAc, the second to its activated form UDP-GlcNAc, and the last yields the polymeric chitin from the amino sugar.


Interference between the effect of N-acetylchitooses and activation by trypsin was also studied. In standard test conditions, microsomal preparations were activated by trypsin at the beginning of the reaction. In a parallel protocol, a preactivation of the microsomal preparation by trypsin was performed, then terminated by addition of trypsin inhibitor. Initial velocity in the presence of N-acetylchitooses clearly reached same value, whether or not trypsinolysis occured before or during chitin polymerization (Figure ). This result excluded a possible effect of chitin synthase protection by N-acetylchitooses against overdigestion by trypsin.

Chitin biosynthesis in Candida albicans grown in vitro …

It has been assumed that most parts of the chitin biosyn-thetic pathway of insects would be similar or identical to the Leloir pathway, which has been worked out extensively in fungi and other microbes (Figure 1). This appears to be the case except for some minor details (Palli and Retnakaran, 1999). The source of the sugar residues for chitin synthesis can be traced to fat body glycogen, which is acted upon by glycogen phosphorylase. Glucose-1-P produced by this reaction is converted to trehalose, which is released into the hemolymph. Trehalose, the extracellular source of sugar in many insect species, is acted upon by a trehalase, which is widely distributed in insect tissues, including the epidermis and gut, to yield intracellular glucose (Becker et al., 1996). This view was recently substantiated by Chen et al. (2010), who showed that the RNAi-induced knockdown of the expression of two treha-lase-encoding genes, SeTrel and SeTre2, caused downregu-lation of the CHS-encoding genes SeCHS1 and SeCHS2, respectively, and led to reduced chitin levels in the cuticle and the PM. The conversion of glucose to fructose-6-P needed for chitin synthesis involves two glycolytic enzymes present in the cytosol. These enzymes are hexokinase and glucose-6-P isomerase, which convert glucose to fructose-6-P. From the latter, the chitin biosynthetic pathway branches off, with the first enzyme catalyzing this branch being glutamine fructose-6-phosphate amidotransferase (GFAT, E. C., which might be thought of as the first committed step in amino sugar biosynthesis. The conversion of fructose-6-P to GlcNAc phosphate involves amination, acetyl transfer, and an isomerization step, which moves the phosphate from C-6 to C-1 (catalyzed by a phospho-N-acetylglucosamine mutase). The conversion of this compound to the nucleotide sugar derivative follows the standard pathway and leads to the formation of an UDP-derivative of GlcNAc, which serves as the substrate for CHS. The entire chitin biosynthetic pathway is outlined in Figure 1. The involvement of dolichol-linked GlcNAc as a precursor for chitin was proposed quite some time ago (Horst, 1983), but that hypothesis has received very limited experimental support (Quesada-Allue, 1982). At this point, this possibility remains unproven. Similarly, the requirement for a primer to which the GlcNAc residues can be transferred also remains speculative. Based on the model for glycogen biosynthesis, which requires glyco-genin as the primer (Gibbons et al., 2002), CHS or an associated protein may fulfill this priming function. Because each sugar residue in chitin is rotated 180° relative to the preceding sugar, which requires CHS to accommodate a alternating "up/down" configuration, another precursor, UDP-chitobiose, has been proposed to be a disaccharide donor during biosynthesis (Chang et al., 2003). Evaluation of radiolabeled UDP-chitobiose as a CHS substrate in yeast, however, revealed that it was not incorporated into chitin. Nevertheless, by testing monomeric and dimeric uridine-derived nucleoside inhibitors as mechanistic probes Yeager and Finney (2004) found a 10-fold greater inhibition for the dimeric inhibitor than the corresponding monomeric inhibitor. However, both inhibitors bound with low affinities in the millimolar range. The stereo-chemical problem in chitin synthesis of adding GlcNAc to the growing chain in two opposite orientations resembles the situation with hyaluronan synthases (HAS), which produce the hyaluronan polymer from two different monosac-charides, UDP-GlcNAc and UDP-glucuronic acid. HASs are "dual action" glycosyltransferases that accomplish hyal-uronan biosynthesis by two substrate-binding and active sites (Weigel and DeAngelis, 2007). As class I HASs are related to chitin synthase, two binding sites for alternating GlcNAc orientations may also occur in CHSs.