Dictionary of Allergies .. Chitinases

Human chitinases (EC.3.2.1.14) are classified into family 18 of glycosyl hydrolase (GH18) superfamily based on their amino acid sequence similarities. Active chitinase hydrolyzes chitin, a beta-1,4-linked N-acetyl-D-glucosamine oligosaccharide. Chitin is a major structural component of the insect exoskeletons and fungal cell walls, but is not found in vertebrates. In human, eight GH18 chitinases have been identified including active chitotriosidase and acidic mammalian chitinase. Most of the human chitinases lack chitinolytic activity due to mutation of an essential glutamic acid residue at the catalytic domain, and they are termed chitolectin[1].

Chitinases hydrolyze the 1-4 linkages of chitin, an unbranched polymer of 1-4 linked N-acetyl-D-glucosamine (GlcNAc). Since chitin is the second most abundant polymer in nature, many organisms including prokaryotes, vertebrates, plants, fungi and insects produce chitinases with roles in nutrition, morphogenesis, aggression and defense.

Plant pathologists are interested in introducing chitinase in plants, in order to make them more resistant to disease. Sensitization to the widespread pathogenesis-related proteins of plants can cause unexpected cross-reactions between foods that are botanically unrelated, as in the case of maize-peach allergy in individuals sensitized to LTPs; another well-known example is the latex-fruit syndrome, which is due to the presence of cross-reacting molecules in latex (Hevea Braziliensis) and in avocado, banana and chestnut.

Many latex allergic patients, in fact, also show IgE binding to these fruits. The main allergens responsible for this cosensitization are class I chitinases, proteins involved in the defence of the plant, which possess an N-terminal hevein-like domain homologous to the major latex allergen Hev b 6.02 [2]. Sanchez-Monge et al. (2000) demonstrated that these allergenic proteins are induced by ethylene, a plant hormone used to accelerate fruit ripening, and destroyed by heat. These findings confirm that industrial treatments can affect the allergenic content of the finished products, and may explain why some plant foods that contain the class I chitinases, but are always cooked before eating, like the green bean (Phaseolus vulgaris), are not usually associated with the latex-fruit syndrome[2].

References

1. Guan SP, Mok YK, Koo KN, Chu KL, Wong WS. Chitinases: biomarkers for human diseases. Chitinases: Protein Pept Lett. 2009;16(5):490-8.

2. Blanco C, Diaz-Perales A, Collada C, et al. Class I chitinases as potential panallergens involved in the latex-frit syndrome. J Allergy Clin Immunol 1999;103:507-513.

3. Cohen-Kupiec, R. and Chet, I. (1998) Current Opinion in Biotechnology 9, 270-277.

Sanchez-Monge R, Blanco C, Diaz Perales A, et al. Class I chitinases, the panallergens responsible for the latex-fruit syndrome, are induced by ethylene treatment and inactivated by heating. J Allergy Clin Immunol 2000;106:190-195.