Richardson Jason S, Oresnik Ivan J
Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
J Bacteriol. 2007 Dec;189(23):8437-46. doi: 10.1128/JB.01032-07. Epub 2007 Sep 21.
Strains of Rhizobium leguminosarum which are unable to catabolize l-rhamnose, a methyl-pentose sugar, are compromised in the ability to compete for nodule occupancy versus wild-type strains. Previous characterization of the 11-kb region necessary for the utilization of rhamnose identified a locus carrying catabolic genes and genes encoding the components of an ABC transporter. Genetic evidence suggested that the putative kinase RhaK carried out the first step in the catabolism of rhamnose. Characterization of this kinase led to the observation that strains carrying rhamnose kinase mutations were unable to transport rhamnose into the cell. The absence of a functional rhamnose kinase did not stop the transcription and translation of the ABC transporter components. By developing an in vitro assay for RhaK activity, we have been able to show that (i) RhaK activity is consistent with RhaK phosphorylating rhamnose and (ii) biochemical activity of RhaK is necessary for rhamnose transport.
不能分解L-鼠李糖（一种甲基戊糖）的豌豆根瘤菌菌株，在与野生型菌株竞争根瘤占据能力方面存在缺陷。先前对利用鼠李糖所需的11kb区域的表征确定了一个携带分解代谢基因和编码ABC转运蛋白组分的基因座。遗传证据表明，推定的激酶RhaK在鼠李糖分解代谢中执行第一步。对该激酶的表征导致观察到携带鼠李糖激酶突变的菌株无法将鼠李糖转运到细胞中。缺乏功能性鼠李糖激酶并不阻止ABC转运蛋白组分的转录和翻译。通过开发一种针对RhaK活性的体外测定方法，我们已经能够证明：（i）RhaK活性与RhaK磷酸化鼠李糖一致；（ii）RhaK的生化活性是鼠李糖转运所必需的。
