Characterization of an ATP Translocase Identified in the Destructive Plant Pathogen “ Candidatus Liberibacter asiaticus”

Abstract

ATP/ADP translocases transport ATP across a lipid bilayer, which is normally impermeable to this molecule due to its size and charge. These transport proteins appear to be unique to mitochondria, plant plastids, and obligate intracellular bacteria. All bacterial ATP/ADP translocases characterized thus far have been found in endosymbionts of protozoa or pathogens of higher-order animals, including humans. A putative ATP/ADP translocase was uncovered during the genomic sequencing of the intracellular plant pathogen "Candidatus Liberibacter asiaticus," the causal agent of citrus huanglongbing. Bioinformatic analysis of the protein revealed 12 transmembrane helices and predicted an isoelectric point of 9.4, both of which are characteristic of this family of proteins. The "Ca. Liberibacter asiaticus" gene (nttA) encoding the translocase was subsequently expressed in Escherichia coli and shown to enable E. coli to import ATP directly into the cell. Competition assays with the heterologous E. coli system demonstrated that the translocase was highly specific for ATP and ADP but that other nucleotides, if present in high concentrations, could also be taken up and/or block the ability of the translocase to import ATP. In addition, a protein homologous to NttA was identified in "Ca. Liberibacter solanacearum," the bacterium associated with potato zebra chip disease. This is the first reported characterization of an ATP translocase from "Ca. Liberibacter asiaticus," indicating that some intracellular bacteria of plants also have the potential to import ATP directly from their environment.

Chlamydia trachomatis Transports NAD via the Npt1 ATP/ADP Translocase

“…While P. amoebophila possesses a dedicated NAD/ADP translocase for this purpose, the chlamydiae possess only two nucleotide transporters belonging to the class I and II NTT families (10,13). While all of the class I and II NTTs previously tested were negative for NAD transport (7,9,11,12,23), the need for NAD transport by chlamydiae led us to examine whether Npt1 Ct , the ATP/ADP translocase, could also transport NAD. Results from our transport kinetic experiments, competition assays, and efflux experiments indicated that Npt1 Ct could transport both NAD (and NADH) and ATP in exchange for ADP.…”

“…NTTs may be divided into three different classes, nucleotide antiporters (class I), proton-driven nucleotide symporters (class II), and NAD/ADP antiporters (class III) (7). NTTs appear to be restricted to a limited number of obligate intracellular bacteria other than the members of the order Chlamydiales, including members of the order Rickettsiales, Lawsonia spp., and "Candidatus Liberbacter spp.," as well as plastids, which all possess ATP/ADP translocases (class I NTTs), presumably to acquire energy from their host (8)(9)(10)(11)(12). To date, class II and III NTTs have been characterized only in Chlamydia trachomatis and P. amoebophila (7,10,13).…”

Nucleotides, micro- and macro-nutrients, limonoids, flavonoids, and hydroxycinnamates composition in the phloem sap of sweet orange

“…9 Analysis of these ABC transporter related proteins by Li et al (2012) showed that CLas uses these ABC transporters to import metabolites and enzyme cofactors. 45 It is also thought that the presence of this large number of transporter proteins might play an important role in providing CLas with necessary nutrients. 9 Besides its ATP synthase CLas also encodes ATP/ADP translocase, which means that CLas can synthesize its own ATP or utilize it directly from its host.…”

“…9 Besides its ATP synthase CLas also encodes ATP/ADP translocase, which means that CLas can synthesize its own ATP or utilize it directly from its host. 23 To test this hypothesis, Vahling et al (2010) expressed the ATP translocase, nucleotide transport protein (NttA) gene encoded by CLas, in Escherichia coli.…”

Nucleotide Parasitism by Simkania negevensis ( Chlamydiae )

“…Among bacteria, NTT proteins catalyzing ATP/ADP exchange have been found in Chlamydiae and Rickettsiales, comprising major intracellular pathogens of humans (15,45,48,62,64,67), and recently also in the obligate intracellular veterinary pathogen Lawsonsia intracellularis belonging to the Deltaproteobacteria (63), in the plant pathogen "Candidatus Liberibacter asiaticus" belonging to the Rhizobiales (75), and in the obligate intracellular amoeba symbiont "Candidatus Amoebophilus asiaticus" belonging to the Bacteroidetes (65). In addition to ATP/ADP translocases, some obligate intracellular bacteria encode nucleotide transport isoforms for the import of nucleotides other than ATP or the cofactor NAD ϩ (7,22,26,27), thereby compensating for their inability to synthesize these metabolites de novo (22,33,66,76).…”