Biochemistry of chitin synthase

Chitin metabolism in insects: structure, function and regulation of chitin synthases and chitinases

“…However, the current evidence for the occurrence of lipidGlcNAc intermediates or acceptors during chitin assembly is weak and therefore not included in the depicted pathway. In fungal systems, at least, an acceptor other than UDP-GlcNAc seems not to be required to initiate polymerization (McMurrough and Bartnicki-Garcia, 1971;Orlean, 1987;Merz et al, 1999a;Chang et al, 2003). Chitin synthase is definitely the key enzyme within the biosynthetic pathway, but detailed understanding of its mode of action seems to be a distant prospect, in particular because the enzyme has not yet been purified to homogeneity.…”

“…enzymes as well. Common features of most chitin synthases are that enzyme activity is dependent on the presence of divalent cations such as Mg 2+ or Mn 2+ and that it is increased by mild proteolysis, suggesting the existence of a zymogenic form (Duran et al, 1975;Mayer et al, 1980;Hardy and Gooday, 1983;Kramer and Koga, 1986;Merz et al, 1999a). Usually, chitin synthase activity can be inhibited by structural UDP-GlcNAc analogues such as polyoxins and nikkomycin (Gooday, 1972;Dahn et al, 1976).…”

“…The resulting dolichyldiphosphate-linked chito-oligomer may act as a GlcNAc acceptor for chitin synthesis (Horst, 1983). By contrast, from kinetic studies it was concluded that chitin synthesis generally occurs without the need for soluble or lipid GlcNAc acceptors functioning as primers for chain assembly (Horsch et al, 1996;Merz et al, 1999a). In line with this interpretation, some groups have reported that chitin synthesis was not affected significantly by tunicamycin in several insect systems (Mayer et al, 1981;Fristrom et al, 1982;Bade, 1983).…”

“…However, even in fungal systems, the significance of this phenomenon has not yet been elucidated (Merz et al, 1999a). Besides proteases, further regulatory factors that affect chitin synthase activity may exist in insects.…”

A chymotrypsin-like serine protease interacts with the chitin synthase from the midgut of the tobacco hornworm

“…It is produced by numerous species belonging to different taxonomic groups, including fungi, molluscs and arthropods. The ability to form chitin strictly depends on the expression of chitin synthase (EC 2.4.1.16), a transmembrane family II glycosyltransferase, which is the key enzyme in chitin metabolism as it catalyses the polymerization of Nacetylglucosamine using uridine-5Ј-diphosphate Nacetylglucosamine as the activated sugar donor (Merz et al, 1999;Merzendorfer, 2006). Due to the lack of sufficient purification procedures and heterologous expression systems, current knowledge on the structure, function and regulation of chitin synthases is still very limited, particularly in insects.…”