Nucleotide transport proteins in bacteria and plant plastids
Responsible scientists: I. Haferkamp, E. Neuhaus
Plant plastids, like chloroplasts and heterotrophic plastids, harbour ATP/ADP-transport proteins (NTT, Nucleotide transporter) exhibiting high structural and functional similarities to nucleotide transporters in intracellular bacteria (Winkler and Neuhaus 1999).
Promoter-GUS-staining of NTT isoforms
Our aim is to identify the function of plastidic nucleotide transporters on the biochemical and physiological level. To characterize these highly hydrophobic membrane proteins we routinely synthesize this group of transporters heterologously in Escherichia coli (Tjaden et al., 1998). It turned out that biochemical properties of recombinant NTT-proteins closely resemble characteristics of authentic proteins in their native membranes (Neuhaus et al., 1998). First structure/function analysis allowed to identify some amino acid residues critical for function (Trentmann et al., 1999).
Physiological implication of plastidic ATP/ADP-transporters have been studied on sense or antisense potato plants (Tjaden et al., 1998) and on knock out plants from Arabidopsis (Reiser et al., 2005). It turned out that the plastidic ATP supply via NTT in potato tubers excert superior control on the rate of starch biosynthesis (Tjaden et al., 1998). In contrast, in Arabidopsis double knock out plants, lacking both functional NTT genes, the level of storage lipid is only reduced by about 40 % of the wildtype level (Reiser et al., 2005). This clearly reveals that the contribution of plastidic ATP/ADP-transport to accumulation of main storage products is strongly species specific. It appears remarkable that Arabidopsis plants with strongly reduced levels of plastidic ATP-import capacity show spontaneous lesions in leaves (unpublished) indicating that alterations in plastid energy metabolism strongly affect plant development.
NTT proteins in bacteria:
The occurrence of transport proteins structurally and functionally similar to plastidic ATP/ADP-transporter in bacteria is fascinating. In fact, up to now bacterial nucleotide transport catalysed by NTT-proteins is limited to obligate intracellular species (Winkler and Neuhaus 1999). We discovered that human pathogenic Chlamydia species contain two NTT isoforms. One acts as a typical ATP/ADP exchanger (connecting host cell energy metabolism to the impaired metabolic machinery of the pathogen), the other is a proton driven nucleoside triphosphate uniporter (Tjaden et al., 1999). The discovery of plastidic ATP/ADP transporters in “primitive” plants like Cyanophora paradoxa (Linka et al., 2003) led us first suppose that this gene originated during plant development. However, detailed phylogenetic analysis clearly indicates that this gene originated in chlamydial ancestors and was horizontally transferred to other bacteria and plants (Schmitz-Esser et al., 2004).
Publications on this subject:
Haferkamp I, Schmitz-Esser S, Linka N, Urbany C, Collingro A, Wagner M, Neuhaus HE (2004) A candidate NAD+ transporter in an intracellular bacterial symbiont related to Chlamydiae. Nature 432: 622-625
Winkler HH, Neuhaus HE (1999) Non-mitochondrial atp transport. TIBS 24: 64-68
Tjaden J, Schwöppe C, Möhlmann T, Neuhaus HE (1998) Expression of the plastidic ATP/ADP transporter gene in Escherichia coli leads to a funtional adenine nucleotide transport system in the bacterial cytoplasmic membrane. J Biol Chem 273: 9630-9636
Tjaden J, Möhlmann T, Kampfenkel K, Henrichs G, Neuhaus HE (1998) Altered plastidic ATP/ADP-transporter activity influences potato (Solanum tuberosum) tuber morphology, yield and composition of tuber starch. Plant J 16: 531-540
Neuhaus HE, Thom E, Möhlmann T, Steup M, Kampfenkel K (1997) Characterization of a novel eukaryotic ATP/ADP translocator located in the plastid envelope of Arabidopsis thaliana L. Plant J 11: 73-82
Trentmann O, Decker C, Winkler HH, Neuhaus HE (2000) Charged amino-acid residues in transmembrane domains of the plastidic ATP/ADP transporter from Arabidopsis are important for transport efficiency, substrate specificity, and counter exchange properties. Eur J Biochem 267: 4098-4105
Reiser J, Linka N, Lemke L, Jeblick W, Neuhaus HE (2004) Molecular physiological analysis of the two plastidic ATP/ADP transporters from Arabidopsis thaliana. Plant Physiol. 136: 3524-3536
Linka N, Hurka H, Lang BF, Burger G, Winkler HH, Stamme C, Urbany C, Seil I, Kusch J, Neuhaus HE (2003) Phylogenetic relationship of non-mitochondrial nucleotide transport proteins in bacteria and eukaryotes. Gene 306: 27-35
Schmitz-Esser S, Linka N, Collingro A, Beier CL, Neuhaus HE, Wagner M, Horn M (2004) ATP/ADP translocases: a common feature of obligate intracellular amoebal symbionts related to Chlamydiae and Rickettsiae. J Bacteriol 186: 683-691
Dr. Peter Geigenberger
MPI für Mol. Pflanzenphysiologie, Golm
Dr. Matthias Horn and Prof. Michael Wagner
Abteilung Mikrobielle Ökologie, Institut für Ökologie und Naturschutz, Universität Wien