Chitin synthesis and inhibition: a revisit

Abstract

Chitin is an abundant biologically important aminopolysaccharide composed of N-acetyl-D-glucosamine units. Individual polymers, which are synthesized intracellularly by chitin synthase (CS), a membrane-bound glycosyl transferase, are translocated across the plasma membrane and coalesce to form rigid crystallites. These crystallites, inter alia, are integral parts of septa and cell walls in yeast and filamentous fungi, respectively, and of cuticles in invertebrates, notably crustaceans and insects. Despite decades of intensive research, many events associated with the complexity of chitin formation and deposition are still obscure, or only partially understood. The list includes the hormonal control of CS at the transcriptional and translational levels as well as the post-translational CS packaging; trafficking and guidance of CS clusters to proper sites in the cells and their intricate insertion into the plasma membranes; activation of the catalytic step and its control or modulation; and translocation of chitin chains across cell membranes, their orientation, fibrillogenesis and association with other extracellular structural components such as polysaccharides (fungi) and cuticular proteins (insects). Also the precise biochemical lesions inflicted by CS inhibitors, such as the acylurea insect growth regulators, are largely unclear. The recent isolation and sequencing of insect CS genes should help in elucidating various aspects of chitin biochemistry and inhibition. In particular, the large number of transmembrane segments, characteristic of the insect CS, are speculated to be involved in chitin translocation and are expected to shed light on the mode of action of acylurea insecticides.

A Review of the Applications of Chitin and Its Derivatives in Agriculture to Modify Plant-Microbial Interactions and Improve Crop Yields

“…This includes trehazolin and allosamidin, two pseudo-saccharides, which are both inhibitors of key enzymes involved in chitin synthesis [148][149][150]. While both trehazolin and allosamidin are effective in vitro, the large number of hydroxy groups in the molecules prevent them penetrating the insect cuticle and reaching their specific targets [151] and this has limited their utilisation for in vivo pest control.…”

“…As chitin is not a biopolymer in vertebrates and is consumed regularly in the human diet, it is considered safe for the control of chitinous pests [149]. Unfortunately there is dearth of information regarding the toxicity of chitin/chitosan to beneficial microbes, nematodes or insects other than those purposely applied as biological control agents alongside chitin products, including saprotrophic/nectrophic organisms.…”

Alterations in the oxidative metabolism of Rhipicephalus (Boophilus) microplus ticks in response to exposure to the insect growth regulator fluazuron

“…Previous studies that have attempted to elucidate the exact mechanism behind the action of benzoylphenylureas gave rise to speculations about their involvement in other pathways. They may affect not only the chitin biosynthesis events (COHEN, 2001), but also others processes, as the inhibition of the glucose conversion into fructose-6-phosphate (PALLI & RETNAKARAN, 1999), an important step known in glycolysis too (NELSON & COX, 2011). However, whether these compounds produced potential consequences to other metabolic pathways involving glucose in ticks (and potential mechanisms of action governing them) had not yet been confirmed.…”

“…However, whether these compounds produced potential consequences to other metabolic pathways involving glucose in ticks (and potential mechanisms of action governing them) had not yet been confirmed. Cohen (2001) stated that fluazuron inhibits glucose phosphorylation process. In accordance to his results, our findings suggested that an imbalance in glucose homeostasis occurs due to the previous inhibition of chitin synthase caused by fluazuron.…”

“…microplus, which spends the entire parasitic part of its life cycle on the same animal, feeding preferentially on cattle (GRAF, 1993). The precise biochemical changes that chitin synthase inhibitors (such as acylurea insect growth regulators) produce in ticks have not yet been well described (COHEN, 2001). It is known that the inhibition of chitin metabolism may disrupt the production of hormones such that morphophysiological changes take place during arthropod development, resulting in the deposition of unviable eggs and the subsequent reduction in the emergence of new individuals (OLIVEIRA et al, 2013).…”