Soemphol Wichai, Toyama Hirohide, Moonmangmee Duangtip, Adachi Osao, Matsushita Kazunobu
Department of Biological Chemistry, Faculty of Agriculture, Yamaguchi University, Yamaguchi 753-8515, Japan.
J Bacteriol. 2007 Jul;189(13):4800-8. doi: 10.1128/JB.01895-06. Epub 2007 Apr 27.
Upstream of the gene for flavin adenine dinucleotide (FAD)-dependent D-sorbitol dehydrogenase (SLDH), sldSLC, a putative transcriptional regulator was found in Gluconobacter frateurii THD32 (NBRC 101656). In this study, the whole sboR gene and the adjacent gene, sboA, were cloned and analyzed. sboR mutation did not affect FAD-SLDH activity in the membrane fractions. The SboA enzyme expressed and purified from an Escherichia coli transformant showed NADPH-dependent L-sorbose reductase (NADPH-SR) activity, and the enzyme was different from the NADPH-SR previously reported for Gluconobacter suboxydans IFO 3291 in molecular size and amino acid sequence. A mutant defective in sboA showed significantly reduced growth on L-sorbose, indicating that the SboA enzyme is required for efficient growth on L-sorbose. The sboR mutant grew on L-sorbose even better than the wild-type strain did, and higher NADPH-SR activity was detected in cytoplasm fractions. Reverse transcription-PCR experiments indicated that sboRA comprises an operon. These data suggest that sboR is involved in the repression of sboA, but not in the induction of sldSLC, on D-sorbitol and that another activator is required for the induction of these genes by D-sorbitol or L-sorbose.
在弗氏葡萄糖杆菌THD32（NBRC 101656）中，在黄素腺嘌呤二核苷酸（FAD）依赖性D - 山梨醇脱氢酶（SLDH）基因sldSLC的上游，发现了一个假定的转录调节因子sboR。在本研究中，克隆并分析了整个sboR基因及其相邻基因sboA。sboR突变不影响膜组分中FAD - SLDH的活性。从大肠杆菌转化体中表达并纯化的SboA酶显示出NADPH依赖性L - 山梨糖还原酶（NADPH - SR）活性，并且该酶在分子大小和氨基酸序列上与先前报道的氧化葡萄糖杆菌IFO 3291的NADPH - SR不同。sboA缺陷型突变体在L - 山梨糖上的生长显著降低，表明SboA酶是在L - 山梨糖上高效生长所必需的。sboR突变体在L - 山梨糖上的生长甚至比野生型菌株更好，并且在细胞质组分中检测到更高的NADPH - SR活性。逆转录 - PCR实验表明sboRA构成一个操纵子。这些数据表明，sboR参与对sboA的抑制，但不参与D - 山梨醇上sldSLC的诱导，并且D - 山梨醇或L - 山梨糖诱导这些基因需要另一种激活剂。
