Phospholipid requirements of membrane-bound chitin synthase fromAbsidia glauca

Biochemistry of chitin synthase

This article compiles the papers dealing with the biochemistry of chitin synthase (CS) published during the last decade, provides up-to-date information on the state of knowledge and understanding of chitin synthesis in vitro, and points out some firmly entrenched ideas and tenets of CS biochemistry that have become of age without hardly ever having been critically re-evaluated. The subject is dealt with under the headings "Components of the CS reaction" (educt, cation requirement and intermediates; product), "Regulation of CS" (cooperativity and allostery; non-allosteric activation or priming of CS; latency), "Concerted action of CS and enzymes of chitinolysis", "Inhibition of CS", "Multiplicity of CSs", and "Structure of CS" (the putative UDPGlcNAc-binding domain of CS; identification of CS polypeptides; glycoconjugation). The prospects are outlined of obtaining a refined three-dimensional (3D) model of the catalytic site of CS for biotechnological applications.

Regulation of chitin synthesis during growth of fungal hyphae: the possible participation of membrane stress

Apical hyphal extension involves very localized apical deposition of newly synthesized wall skeletal material, notably chitin. A branch forms where a new localized site of chitin deposition occurs in the lateral wall. Key enzymes involved are the chitin synthases. Their activity must be under tight regulation to achieve the orderly deposition of chitin. There is evidence that inactive chitin synthase is distributed throughout the hyphal plasma membrane and activated at the apex and at an incipient branch site. At these sites, the wall is plastic. We have investigated the hypothesis that physical stressing of the membrane, a consequence of the cell's turgor pressure acting at these weaker points, may locally activate the chitin synthase. Results show that cells that have been subjected to hypoosmotic stress have raised native chitin synthase activities. It is suggested that stressing the membrane may cause a conformational change in chitin synthase molecules in the membrane or changes in the interactions between chitin synthase and associated polypeptides, leading to activation. This process may act along with other regulatory mechanisms discussed here, such as post-translational modification and availability of allosteric effectors, to restrict the enzymic activity to sites where chitin synthesis is required. Key words: chitin synthase, zymogen, turgor pressure, membrane stress, Candida albicans, hyphal growth.