Article

Chitinolytic Enzymes: Catalysis, Substrate Binding, and their Application

Laboratory of Biophysical Chemistry, Faculty of Agriculture, Kinki University, 3327-204 Nakamachi, Nara 631-8505, Japan.
Current Protein and Peptide Science (Impact Factor: 2.33). 07/2000; 1(1):105-24. DOI: 10.2174/1389203003381450
Source: PubMed

ABSTRACT After the epoch-making report on X-ray crystal structure of a lysozyme-N-acetylglucosamine trisaccharide complex in 1967, catalytic mechanisms of glycosyl hydrolases have been discussed with reference to the lysozyme mechanism. From the recent findings of chitinolytic enzymes, however, the enzymes were found to have catalytic and substrate binding mechanisms different from those of lysozyme. Based on the X-ray crystal structures of chitinases and their complexes with substrate analogues, the catalytic mechanisms were discussed considering the relative locations of catalytic residues to the bound substrate analogues. Resembling the lysozyme catalytic center, family 19 chitinases, family 46 chitosanases, and family 23 lysozymes have two carboxyl groups at the catalytic center, which are separated (> 10 +) on either side of the catalytic cleft. The catalytic reaction of the enzymes takes place through a single displacement mechanism. In family 18 chitinases, one can identify only one catalytic carboxylate as a proton donor, but not the second catalytic carboxylate whose function and location are similar to those of Asp52 in lysozyme. The catalytic reaction of family 18 chitinases is most likely to take place through a substrate-assisted mechanism. Hen egg white lysozyme has the binding cleft represented by (-4)(-3)(-2)(-1)(+1)(+2). The binding cleft of family 19 chitinases, family 46 chitosanases, and family 23 lysozymes, however, is represented by (-3)(-2)(-1)(+1)(+2)(+3). Molecular dynamics calculation suggests that family 18 chitinases have the binding cleft, (-4)(-3)(-2)(-1)(+1)(+2). The functional diversity of the chitinolytic enzymes might be related to different physiological functions of the enzymes. The enzymes are now being applied to plant protection from fungal pathogens and insect pests. Structure of the targeted chitinous component was determined by a combination of enzyme digestion and solid state CP/MAS NMR spectroscopy, and have been taken into consideration for efficient application of the enzymes. Recent understanding of the catalytic and substrate binding mechanisms would be helpful as well for arrangement of a powerful strategy in such an application.

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    • "In nature degradation of chitin is a slow process and involves a cascade of pathways. Chitinases are reported in the moulting fluid of arthropods and are mainly used to digest the structural polysaccharides in their gut linings and exoskeleton during moulting (Karmer et al. 1985; Fukamizo & Kramer 1985; Karmer & Muthukrishnan 1997; Fukamizo 2000). The present study aimed at understanding the influence of chitinase enzyme on the degradation of nauplii of barnacle, Balanus amphitrite Darwin, 1854 at different time interval . "
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    • "Based on amino acid sequence similarity of the catalytic domain, chitinases are classified into family-18 and -19 glycosyl hydrolases in the Carbohydrate-Active enZymes CAZy databases (http://www.cazy.org) (Henrissat and Davies, 1997; Fukamizo, 2000). The chitinase 18 family is found in a wide variety of organisms, including bacteria, archaea, fungi, some plants, insects, animals as well as viruses. "
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