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Truncation of class IV chitinases from Arabidopsis by secreted fungal proteases

NAUMANN, Todd A., PRICE, Neil P. J.
Molecular plant pathology 2012 v.13 no.9 pp. 1135
Alternaria brassicae, Arabidopsis thaliana, Fusarium verticillioides, Pichia pastoris, Zea mays, active sites, chitin, chitinase, cole crops, fungi, pathogenicity, pathogens, polymerization, protein secretion, proteinases
Plant class IV chitinases have a small, amino-terminal chitin binding domain and a larger chitinase domain. Previous work on Zea mays chitinases ChitA and ChitB showed that their chitin binding domains bind insoluble chitin, that their catalytic domains degrade short, soluble forms of chitin, and that the chitin-binding domain is removed by proteases secreted by fungal pathogens. Here we analyze four chitinases from the model dicot Arabidopsis thaliana. We show that some of their chitin-binding domains bind insoluble chitin and that their chitinase domains degrade short, soluble forms of chitin and catalyze transglycosylation. Moreover, the chitin binding domain of some can be removed by Fv-cmp, a fungalysin protease produced by Fusarium verticillioides. Recombinant chitinases were expressed in Pichia pastoris. The basic chitinases AtchitIV3 and AtchitIV4 were purified by chitin affinity. Acidic chitinases AtchitIV1 and AtchitIV5 did not bind insoluble chitin, and were purified by other methods. The recombinant chitinases all degraded GlcNAc oligomers with degree of polymerization (dp) 6. The four chitinases also produced dp5 without production of dp1, indicating transglycosylation activity. Incubation of chitinases with Fv-cmp resulted in truncation of AtchitIV3 and AtchitIV5 while incubation with secreted proteins from Alternaria brassicae, a pathogen of A. thaliana and brassica crops, led to trunction of AtchitIV3 and AtchitIV4. Our finding that both A. thaliana and Z. mays class IV chitinases are truncated by proteases secreted by specialized pathogens of each plant suggests that this is a general mechanism of fungal pathogenicity.