Jonsson Anders, Nordlund Stefan
Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
J Bacteriol. 2007 May;189(9):3471-8. doi: 10.1128/JB.01704-06. Epub 2007 Mar 2.
P(II) proteins have been shown to be key players in the regulation of nitrogen fixation and ammonia assimilation in bacteria. The mode by which these proteins act as signals is by being in either a form modified by UMP or the unmodified form. The modification, as well as demodification, is catalyzed by a bifunctional enzyme encoded by the glnD gene. The regulation of this enzyme is thus of central importance. In Rhodospirillum rubrum, three P(II) paralogs have been identified. In this study, we have used purified GlnD and P(II) proteins from R. rubrum, and we show that for the uridylylation activity of R. rubrum GlnD, alpha-ketoglutarate is the main signal, whereas glutamine has no effect. This is in contrast to, e.g., the Escherichia coli system. Furthermore, we show that all three P(II) proteins are uridylylated, although the efficiency is dependent on the cation present. This difference may be of importance in understanding the effects of the P(II) proteins on the different target enzymes. Furthermore, we show that the deuridylylation reaction is greatly stimulated by glutamine and that Mn(2+) is required.
P(II)蛋白已被证明是细菌中固氮和氨同化调节的关键参与者。这些蛋白作为信号发挥作用的方式是处于被UMP修饰的形式或未修饰的形式。这种修饰以及去修饰由glnD基因编码的双功能酶催化。因此，对这种酶的调节至关重要。在深红红螺菌中，已鉴定出三种P(II)旁系同源物。在本研究中，我们使用了从深红红螺菌中纯化的GlnD和P(II)蛋白，并且我们表明，对于深红红螺菌GlnD的尿苷酰化活性，α-酮戊二酸是主要信号，而谷氨酰胺没有影响。这与例如大肠杆菌系统形成对比。此外，我们表明所有三种P(II)蛋白都被尿苷酰化，尽管效率取决于存在的阳离子。这种差异可能对于理解P(II)蛋白对不同靶酶的影响很重要。此外，我们表明谷氨酰胺极大地刺激了去尿苷酰化反应，并且需要Mn(2+)。
