Lu Q, Park H, Egger L A, Inouye M
Department of Biochemistry, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
J Biol Chem. 1996 Dec 20;271(51):32886-93. doi: 10.1074/jbc.271.51.32886.
Nucleoside-diphosphate kinase (NDP kinase), a key enzyme in nucleotide metabolism, is also known to be involved in growth and developmental control and tumor metastasis suppression. Interestingly, we find that coexpression of NDP kinase with Taz1, a Tar/EnvZ chimera, in the absence of its native signal, can activate a porin gene ompC-lacZ expression in Escherichia coli. Further studies show that NDP kinase can act as a protein kinase to phosphorylate histidine protein kinases such as EnvZ and CheA which are members of the His-Asp phosphorelay signal transduction systems in E. coli. Instead of ATP, the exclusive phosphodonor for histidine kinases, GTP can be utilized in vitro in the presence of NDP kinase to phosphorylate EnvZ and CheA, which then transfer the phosphoryl group to OmpR and CheY, the respective response regulators. The direct involvement of GTP for the phosphorylation of EnvZ through NDP kinase was further demonstrated by the use of a mutant EnvZ, which lost ability to be autophosphorylated with ATP. Phospho-OmpR thus formed can bind specifically to an ompF promoter sequence. These results suggest that NDP kinase may play a physiological role in signal transduction.
核苷二磷酸激酶（NDP激酶）是核苷酸代谢中的关键酶，也已知其参与生长发育调控和肿瘤转移抑制。有趣的是，我们发现，在没有其天然信号的情况下，NDP激酶与Tar/EnvZ嵌合体Taz1共表达，可激活大肠杆菌中孔蛋白基因ompC-lacZ的表达。进一步研究表明，NDP激酶可作为一种蛋白激酶，使组氨酸蛋白激酶如EnvZ和CheA磷酸化，它们是大肠杆菌中His-Asp磷酸化信号转导系统的成员。在NDP激酶存在的情况下，体外可利用GTP而非组氨酸激酶唯一的磷酸供体ATP，使EnvZ和CheA磷酸化，然后它们将磷酸基团转移至各自的应答调节因子OmpR和CheY。通过使用一种丧失了被ATP自身磷酸化能力的突变型EnvZ，进一步证明了GTP通过NDP激酶直接参与EnvZ的磷酸化。由此形成的磷酸化OmpR可特异性结合ompF启动子序列。这些结果表明，NDP激酶可能在信号转导中发挥生理作用。
