Experimental evidence for the thermophilicity of ancestral life.

Theoretical studies have focused on the environmental temperature of the universal common ancestor of life with conflicting conclusions. Here we provide experimental support for the existence of a thermophilic universal common ancestor. We present the thermal stabilities and catalytic efficiencies of nucleoside diphosphate kinases (NDK), designed using the information contained in predictive phylogenetic trees, that seem to represent the last common ancestors of Archaea and of Bacteria. These enzymes display extreme thermal stabilities, suggesting thermophilic ancestries for Archaea and Bacteria. The results are robust to the uncertainties associated with the sequence predictions and to the tree topologies used to infer the ancestral sequences. Moreover, mutagenesis experiments suggest that the universal ancestor also possessed a very thermostable NDK. Because, as we show, the stability of an NDK is directly related to the environmental temperature of its host organism, our results indicate that the last common ancestor of extant life was a thermophile that flourished at a very high temperature.

Putative functions of nucleoside diphosphate kinase in plants and fungi.

The putative functions of NDP (nucleoside diaphosphate) kinases from various organisms focusing to fungi and plants are described. The biochemical reactions catalyzed by NDP kinase are as follows. (i) Phosphotransferring activity from mainly ATP to cognate NDPs generating nucleoside triphosphates (NTPs). (ii) Autophosphorylation activity from ATP and GTP. (iii) Protein kinase (phosphotransferring) activity phosphorylating such as myelin basic protein. NDP kinase could function to provide NTPs as a housekeeping enzyme. However, recent works proved possible functions of the NDP kinases in the processes of signal transduction in various organisms, as described below. 1) By use of the extracts of the mycelia of a filamentous fungus Neurospora crassa blue-light irradiation could increase the phosphorylation of a 15-kDa protein, which was purified and identified to be NDP kinase (NDK-1). By use of the etiolated seedlings of Pisum sativum cv Alaska and Oryza sativa red-light irradiation of intact plants increased the phosphorylation of NDP kinase. However, successive irradiation by red-far-red reversed the reaction, indicating that phytochrome-mediated light signals are transduced to the phosphorylation of NDP kinase. 2) NDP kinase localizing in mitochondria is encoded by nuclear genome and different from those localized in cytoplasm. NDP kinase in mitochondria formed a complex with succinyl CoA synthetase. 3) In Spinicia oleraceae two different NDP kinases were detected in the chloroplast, and in Pisum sativum two forms of NDP kinase originated from single species of mRNA could be detected in the choloroplast. However, the function of NDP kinases in the choloroplast is not yet known. 4) In Neurospora crassa a Pro72His mutation in NDP kinase (ndk-1Pro72His) deficient in the autophosphorylation and protein kinase activity resulted in lacking the light-induced polarity of perithecia. In wild-type directional light irradiation parallel to the solid medium resulted in the formation of the perithecial beak at the top of perithecia, which was designated as "light-induced polarity of perithecia." In wild-type in darkness the beak was formed at random places on perithecia, and in ndkPro72His mutant the perithecial beak was formed at random places even under directional light illumination. The introduction of genomic DNA and cDNA for ndk-1 demonstrated that the wild-type DNAs suppressed the mutant phenotype. With all these results except for the demonstration in Neurospora, most of the phenomena are elusive and should be solved in the molecular levels concerning with NDP kinases.

Protein interactions provide new insight into Nm23/nucleoside diphosphate kinase functions.

Nm23-NDPKs besides contributing to the maintenance of the cellular nucleoside triphosphate pool, exert regulatory properties in a variety of cellular events including proliferation, invasiveness, development, differentiation, and gene regulation. This review focuses on recently discovered protein-protein interactions involving the Nm23 proteins. The findings herein summarized provide new and intriguing suggestions for a more extensive understanding of the biological functions of the Nm23 proteins.

The human Nm23/nucleoside diphosphate kinases.

Biochemical experiments over the past 40 years have shown that nucleoside diphosphate (NDP) kinase activity, which catalyzes phosphoryl transfer from a nucleoside triphosphate to a nucleoside diphosphate, is ubiquitously found in organisms from bacteria to human. Over the past 10 years, eight human genes of the nm23/NDP kinase family have been discovered that can be separated into two groups based on analysis of their sequences. In addition to catalysis, which may not be exhibited by all isoforms, evidence for regulatory roles has come recently from the discovery of the genes nm23 and awd, which encode NDP kinases and are involved in tumor metastasis and Drosophila development, respectively. Current work shows that the human NDP kinase genes are differentially expressed in tissues and that their products are targeted to different subcellular locations. This suggests that Nm23/NDP kinases possess different, but specific, functions within the cell, depending on their localization. The roles of NDP kinases in metabolic pathways and nucleic acid synthesis are discussed.