title: Enzymatic characterization of scytalone dehydratase Val75Met variant found in melanin biosynthesis dehydratase inhibitor (MBI-D) resistant strains of the rice blast fungus.
abstract: Carpropamid ((1RS,3SR)-2,2-dichloro-N-[(R)-1-(4-chlorophenyl)ethyl]-1-ethyl-3-methylcyclopropanecarboxamide) is a potent chemical against the rice blast fungus, Pyricularia oryzae. In 2001, isolates of the fungus with reduced sensitivity to this fungicide appeared in Saga Prefecture of Japan and were regarded as a potential threat to rice protection by carpropamid. The cause of the resistance has been identified genetically as a point mutation resulting in the Val75Met change in scytalone dehydratase, the primary target of the fungicide. We constructed an overexpression system of the variant enzyme and characterized the kinetics in the catalysis and the inhibition by carpropamid isomers. The variant enzyme retained a significant level of enzymatic activity. Inhibition of the variant enzyme by carpropamid was more than 200-fold reduced in comparison with that of the wild-type. Based on the results, here we propose possible mechanisms of the carpropamid-resistance of the variant enzyme in retaining the normal enzymatic activity.
authors.affiliation: Department of Physics, Faculty of Science and Technology, Keio University, Yokohama, Kanagawa, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Yamada
authors.forename: Takayuki
authors.initials: T
authors.lastname: Motoyama
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Nakasako
authors.forename: Shinzo
authors.initials: S
authors.lastname: Kagabu
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Kudo
authors.forename: Isamu
authors.initials: I
authors.lastname: Yamaguchi
mesh_terms: D000577:Amides / Q000494:pharmacology*; D019943:Amino Acid Substitution; D000935:Antifungal Agents / Q000494:pharmacology*; D003001:Cloning, Molecular; D003521:Cyclopropanes / Q000494:pharmacology*; D025141:Drug Resistance, Fungal / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D006836:Hydro-Lyases / Q000037:antagonists & inhibitors* / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D020082:Magnaporthe / Q000187:drug effects / Q000201:enzymology* / Q000472:pathogenicity; D008543:Melanins / Q000096:biosynthesis; D015394:Molecular Structure; D012275:Oryza / Q000382:microbiology; D010935:Plant Diseases / Q000382:microbiology; D017354:Point Mutation / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification
chemical_list: D000577:Amides; D000935:Antifungal Agents; D003521:Cyclopropanes; D004791:Enzyme Inhibitors; D008543:Melanins; D011994:Recombinant Proteins; D006836:Hydro-Lyases; C082741:scytalone dehydratase; C113565:carpropamid