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Báo cáo khoa học: Substrate specificity and inhibition of brassinin hydrolases, detoxifying enzymes from the plant pathogens Leptosphaeria maculans and Alternaria brassicicola

Blackleg (Leptosphaeria maculansand Leptosphaeria biglobosa) and black spot (Alternaria brassicicola) fungi are devastating plant pathogens known to detoxify the plant defence metabolite, brassinin. The significant roles of brassinin as a crucifer phytoalexin and as a biosynthetic precursor of sev-eral other plant defences make it important in plant fitness. | Substrate specificity and inhibition of brassinin hydrolases detoxifying enzymes from the plant pathogens Leptosphaeria maculans and Alternaria brassicicola M. Soledade C. Pedras Zoran Minic and Vijay K. Sarma-Mamillapalle Department of Chemistry University of Saskatchewan Saskatoon Canada Keywords brassinin cyclobrassinin detoxification dithiocarbamate hydrolase phytoalexin Correspondence M. S. C. Pedras Department of Chemistry University of Saskatchewan 110 Science Place Saskatoon SK Canada S7N 5C9 Fax 1 306 966 4730 Tel 1 306 966 4772 E-mail s.pedras@usask.ca Received 6 May 2009 revised 26 September 2009 accepted 22 October 2009 doi 10.1111 j.1742-4658.2009.07457.x Blackleg Leptosphaeria maculans and Leptosphaeria biglobosa and black spot Alternaria brassicicola fungi are devastating plant pathogens known to detoxify the plant defence metabolite brassinin. The significant roles of brassinin as a crucifer phytoalexin and as a biosynthetic precursor of several other plant defences make it important in plant fitness. Brassinin detoxifying enzymes produced by L. maculans and A. brassicicola catalyse the detoxification of brassinin by hydrolysis of its dithiocarbamate group to indolyl-3-methanamine. The purification and characterization of brassinin hydrolases produced by L. maculans BHLmL2 and A. brassicicola BHAb were accomplished native BHLmL2 was found to be a tetrameric protein with a molecular mass of 220 kDa whereas native BHAb was found to be a dimeric protein of 120 kDa. Protein characterization using LC-MS MS and sequence alignment analyses suggested that both enzymes belong to the family of amidases with the catalytic Ser Ser Lys triad. Furthermore chemical modification of BHLmL2 and BHAb with selective reagents suggested that the amino acid serine was involved in the catalytic activity of both enzymes. The overall results indicated that BHs have new substrate specificities with a new catalytic activity that can be designated as dithiocarbamate hydrolase.