Characterization of a thermostable NADPH:FMN oxidoreductase from the mesophilic bacterium Bacillus subtilis

被引:46
作者
Deller, Sigrid
Sollner, Sonja
Trenker-El-Toukhy, Rosemarie
Jelesarov, Ilian
Guebitz, Georg M.
Macheroux, Peter
机构
[1] Graz Univ Technol, Inst Biochem, A-8010 Graz, Austria
[2] Univ Zurich, Inst Biochem, CH-8057 Zurich, Switzerland
[3] Graz Univ Technol, Inst Environm Biotechnol, A-8010 Graz, Austria
基金
奥地利科学基金会;
关键词
D O I
10.1021/bi052478r
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The gene yhdA from Bacillus subtilis encoding a putative flavin mononucleotide ( FMN)-dependent oxidoreductase was cloned and heterologously expressed in Escherichia coli. The purified enzyme has a noncovalently bound FMN cofactor, which is preferentially reduced by NADPH, indicating that YhdA is a NADPH: FMN oxidoreductase. The rate of NADPH oxidation is enhanced by the addition of external FMN, and analysis of initial rate measurements reveals the occurrence of a ternary complex in a bi-bi reaction mechanism. YhdA has also been shown to reductively cleave the -N=N- bond in azo dyes at the expense of NADPH, and hence, it possesses azoreductase activity, however, at a rate 100 times slower than that found for FMN. Using Cibacron Marine as a model compound, we could demonstrate that the dye is a competitive inhibitor of NADPH and FMN. The utilization of NADPH and the absence of a flavin semiquinone radical distinguish YhdA from flavodoxins, which adopt the same structural fold, i. e., a five-stranded beta sheet sandwiched by five alpha helices. The native molecular-mass of YhdA was determined to be 76 kDa, suggesting that the protein occurs as a tetramer, whereas the YhdA homologue in Saccharomyces cerevisiae ( YLR011wp) forms a dimer in solution. Interestingly, the different oligomerization of these homologous proteins correlates to their thermostability, with YhdA exhibiting a melting point of 86.5 degrees C, which is 26.3 degrees C higher than that for the yeast protein. This unusually high melting point is proposed to be the result of increased hydrophobic packing between dimers and the additional presence of four salt bridges stabilizing the dimer-dimer interface.
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收藏
页码:7083 / 7091
页数:9
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