Chitinases and Peptide Mimotopes

high-affinity chitin binding region [4]. Five homologs of the plant chitinases have been identified in A. fumiga-tus. Only one member of this family has a putative GPI anchor and associated cleavage site (http://www.tigr. org/tdb/e2k1/afu1/), suggesting that this enzyme may Inhibition of glycosylhydrolases by peptides mimick-function in morphogenesis since most of the GPI an-ing carbohydrates opens a new field in antifungal re-chored proteins of A. fumigatus have a putative role in search. cell wall construction [5]. Disruption of the ortholog of this gene in A. nidulans leads indeed to a decrease in The manuscript of Rao et al. [1] is a detailed study of the frequency of spore germination and a lower rate of the interactions between two cyclopentapeptides, ar-hyphal formation [6]. In A. fumigatus, the role of the four gifin and argafin, and a " bacterial " chitinase secreted other plant chitinases will await the disruption of their by the fungus Aspergillus fumigatus. encoding genes [4]. Although analyzing the interactions Chitin is one of the major structural components of of inhibitor peptides with a chitinase that have a role in the cell wall of fungi and the exoskeleton of animals. morphogenesis would have been more appropriate in The presence of chitin in the extracellular matrix of the study of Rao et al., the results obtained with ChiB1 fungi is in total agreement with the animal origin of should be easily compared with plant chitinases. The fungi. Over time, enzymes associated with the synthe-3D structure has been determined for various chi-sis and remodeling of this polysaccharide have evolved tinases [7]; data of all families substantiate the strict in number and complexity. Recent surveys of fungal ge-conservation of the catalytic machinery, show the cleft nomes have shown that A. fumigatus, whose genome structure in the active site, and show that substrate de-is one of the most recently defined among the filamen-gradation occurs with retention of the configuration at tous fungi, has 8 chitin synthase and 18 chitinase genes the anomeric carbon. Sequence similarities are also whereas only 3 and 2 respectively have been found in confirmed biologically since anti-human chitinase anti-yeasts. bodies have been shown by immunofluorescence At some point during their complex life cycle, such as studies to label the tip of A. fumigatus conidial germ cytokinesis in yeast and conidial germination or hyphal tubes (J.-P. Latgé, unpublished data). branching in molds, all pathogenic fungi have to hy-The two cyclopentapeptides described …