Overall intracellular ADPR content,including both the free and the protein-bound forms, is in the low millimolar range [22]. It is well known that free ADPR is a highly reactive molecule that causes non-enzymatic glycation of proteins, leading to loss of function [37]; on the other hand, recent evidence in both eukaryotes and bacteria shows that ADPR acts as a cellular signal [13,38,39]. In particular, in bacteria, it functions as a signal of NAD pool consumption promoting transcription of NAD biosynthetic genes through its binding to the NrtR repressor [39]. In this view, ADPRPs represent not just “housecleaning enzymes”, merely scavenging potentially toxic ADPR, but also important players in ADPR signaling. In addition, their fusion to NADsynthesizing enzymes suggests their direct contribution to NAD regeneration. The genomic context analysis of the ADPRP(COG1058)/pncC gene shows that it is most frequently associated in predicted operons with the recombinase gene recA and genes coding for enzymes involved in various aspects of DNA/RNA metabolism, including RNA repair. Interestingly, in some d-proteobacteria and in the Deinococcus/Thermus group, ADPRP(COG1058)/pncC and recA are associated in a polycistronic operon with the gene ligT, encoding the enzyme 29-59 RNA ligase, which is capable of joining in vitro yeast tRNAs splicing intermediates to form internal 29-59 linkages, and whose role in bacterial RNA repair has been recently postulated [40,41]. In the Deinococcus/Thermus group, such operon is further extended to include a gene encoding a protein of the YgfZ family, known to participate in the repair of iron/sulphur clusters, hence involved in maintaining the activity of several Fe-S enzymes, including the enzyme MiaB responsible of the methylthiolation of tRNA [42]. The presence of the ADPRP(COG1058)/pncC gene in such operons might be indicative of the requirement of NMN deamidase and ADPRP activities during RecA-dependent processes likely involved in DNA/RNA repair. The former would scavenge NMN, a potent inhibitor of the NAD-dependent DNA ligase, ensuring, at the same time, NADCOG1058 Is a Novel Pyrophosphatase Familysupply to the ligase reaction [10]; the ADPR activity, in turn, might be involved in the scavenging of free ADPR. Indeed, the occurrence in bacteria 23148522 of ADPR-producing processes during nucleic acids repair has been recently supported by bioinformatic predictions [43]. In addition, in Deinococcus radiodurans cells a marked induction of the operon ADPRP(COG1058)/MedChemExpress CASIN pncC-recA-ligT has been observed after irradiation or desiccation [41,44], and a Streptococcus K162 site mutans strain deleted of ADPRP(COG1058)/pncC shows a significant increase in the sensitivity to DNA damaging agents [45]. Finally, the proposed role of the bacterial (COG1058)ADPRP in the scavenging of ADPR during DNA/RNA repair processes is in keeping with the marked increase of the ADP-ribosyltransferase activity observed in several bacterial species in response to DNA damage [46]. In this work we have identified as ADPRPs both the SoCOG1058 domain fused to NMN deamidase and the standalone AtCOG1058 domain. These results, together with those derived from the multiple sequence analysis performed on the whole COG1058 and confirmed by the mutagenesis experiments, enabled us to extend the assignment of the pyrophosphatase function to all COG1058 members, with the apparent exception of plant proteins that lack conservation of catalytic residues. COG1058 pyrophosphatase.Overall intracellular ADPR content,including both the free and the protein-bound forms, is in the low millimolar range [22]. It is well known that free ADPR is a highly reactive molecule that causes non-enzymatic glycation of proteins, leading to loss of function [37]; on the other hand, recent evidence in both eukaryotes and bacteria shows that ADPR acts as a cellular signal [13,38,39]. In particular, in bacteria, it functions as a signal of NAD pool consumption promoting transcription of NAD biosynthetic genes through its binding to the NrtR repressor [39]. In this view, ADPRPs represent not just “housecleaning enzymes”, merely scavenging potentially toxic ADPR, but also important players in ADPR signaling. In addition, their fusion to NADsynthesizing enzymes suggests their direct contribution to NAD regeneration. The genomic context analysis of the ADPRP(COG1058)/pncC gene shows that it is most frequently associated in predicted operons with the recombinase gene recA and genes coding for enzymes involved in various aspects of DNA/RNA metabolism, including RNA repair. Interestingly, in some d-proteobacteria and in the Deinococcus/Thermus group, ADPRP(COG1058)/pncC and recA are associated in a polycistronic operon with the gene ligT, encoding the enzyme 29-59 RNA ligase, which is capable of joining in vitro yeast tRNAs splicing intermediates to form internal 29-59 linkages, and whose role in bacterial RNA repair has been recently postulated [40,41]. In the Deinococcus/Thermus group, such operon is further extended to include a gene encoding a protein of the YgfZ family, known to participate in the repair of iron/sulphur clusters, hence involved in maintaining the activity of several Fe-S enzymes, including the enzyme MiaB responsible of the methylthiolation of tRNA [42]. The presence of the ADPRP(COG1058)/pncC gene in such operons might be indicative of the requirement of NMN deamidase and ADPRP activities during RecA-dependent processes likely involved in DNA/RNA repair. The former would scavenge NMN, a potent inhibitor of the NAD-dependent DNA ligase, ensuring, at the same time, NADCOG1058 Is a Novel Pyrophosphatase Familysupply to the ligase reaction [10]; the ADPR activity, in turn, might be involved in the scavenging of free ADPR. Indeed, the occurrence in bacteria 23148522 of ADPR-producing processes during nucleic acids repair has been recently supported by bioinformatic predictions [43]. In addition, in Deinococcus radiodurans cells a marked induction of the operon ADPRP(COG1058)/pncC-recA-ligT has been observed after irradiation or desiccation [41,44], and a Streptococcus mutans strain deleted of ADPRP(COG1058)/pncC shows a significant increase in the sensitivity to DNA damaging agents [45]. Finally, the proposed role of the bacterial (COG1058)ADPRP in the scavenging of ADPR during DNA/RNA repair processes is in keeping with the marked increase of the ADP-ribosyltransferase activity observed in several bacterial species in response to DNA damage [46]. In this work we have identified as ADPRPs both the SoCOG1058 domain fused to NMN deamidase and the standalone AtCOG1058 domain. These results, together with those derived from the multiple sequence analysis performed on the whole COG1058 and confirmed by the mutagenesis experiments, enabled us to extend the assignment of the pyrophosphatase function to all COG1058 members, with the apparent exception of plant proteins that lack conservation of catalytic residues. COG1058 pyrophosphatase.
