Open AccessDifferent substrate specificities of two triazine hydrolases (TrzNs) from Nocardioides species
Author(s) -
Yamazaki Kenichi,
Fujii Kunihiko,
Iwasaki Akio,
Takagi Kazuhiro,
Satsuma Koji,
Harada Naoki,
Uchimura Tai
Publication year - 2008
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.2008.01271.x
Subject(s) - atrazine , triazine , escherichia coli , biology , strain (injury) , biochemistry , chemistry , mutant , amino acid , actinomycetales , gene , stereochemistry , bacteria , streptomyces , genetics , organic chemistry , anatomy , pesticide , agronomy
Nocardioides sp. strain MTD22 degraded atrazine, ametryn and atraton, as did Arthrobacter aurescens strain TC1 and Nocardioides sp. strain C190. These strains contain trzN , a gene coding for TrzN, triazine hydrolase showing a broad substrate range. However, Nocardioides sp. strain AN3 degraded only atrazine despite containing trzN . These differences in s ‐triazine degradation are presumed to be due to differences in the amino acid sequences of TrzNs. Consequently, 1371 nucleotides of the trzN coding sequences of strains AN3 and MTD22 were determined. Comparisons of the amino acid sequences of TrzNs indicated that three residues of strain AN3 (Thr 214 , His 215 and Gln 241 ) were distinct from those of the other three strains (Pro 214 , Tyr 215 and Glu 241 ). To confirm the relationships between these amino acid sequences and the substrate specificities of TrzNs, wild and chimera trzN genes were constructed and expressed in Escherichia coli cells. Cells expressing wild MTD22 trzN (Pro 214 Tyr 215 Glu 241 ) and chimera AN3–MTD22 trzN (Thr 214 His 215 Glu 241 ) degraded all s ‐triazines, but the degradation rate was markedly decreased in AN3–MTD22 trzN . Wild AN3 trzN (Thr 214 His 215 Gln 241 ) and chimera MTD22–AN3 trzN (Pro 214 Tyr 215 Gln 241 ) degraded only atrazine. These results suggest that the substitution of Glu 241 for Gln 241 significantly decreases enzyme affinity for ametryn and atraton.