Different ways of doing the same: Variations in the two last steps of the purine biosynthetic pathway in prokaryotes

Abstract

The last two steps of the purine biosynthetic pathwaymay be catalyzed by different enzymes in prokaryotes. The genes that encode these enzymes include homologs of purH, purP, purO and those encoding the AICARFT and IMPCH domains of PurH, here named purV and purJ, respectively. InBacteria, these reactions aremainly catalyzedby thedomainsAICARFT andIMPCHof PurH. InArchaea, these reactions may be carried out by PurH and also by PurP and PurO, both considered signatures of this domain and analogous to the AICARFT and IMPCH domains of PurH, respectively. These geneswere searched for in 1,403 completely sequenced prokaryotic genomes publicly available.Our analyses revealed taxonomic patterns for the distribution of these genes and anticorrelations in their occurrence. The analyses of bacterial genomes revealed the existence of genes coding for PurV, PurJ, and PurO,whichmay no longer be considered signatures of the domain Archaea.Although highly divergent, the PurOs of Archaea and Bacteria showa high level of conservation in the amino acids of the active sites of the protein, allowing us to infer that these enzymes are analogs. Based on the results, we propose that the gene purO was present in the common ancestor of all living beings, whereas the gene encoding PurP emerged after the divergence of Archaea and Bacteria and their isoformsoriginated in duplication events in the common ancestor of phylaCrenarchaeotaandEuryarchaeota.Theresults reportedhere expandourunderstanding of thediversity andevolutionof the last two steps of the purine biosynthetic pathway in prokaryotes.