Purine Catabolism in Escherichia coli and Function of Xanthine Dehydrogenase in Purine Salvage

Abstract

Escherichia coli is not known to utilize purines, other than adenine and adenosine, as nitrogen sources. We reinvestigated purine catabolism because a computer analysis suggested several potential 54 -dependent promoters within a 23-gene cluster whose products have homology to purine catabolic enzymes. Our results did not provide conclusive evidence that the 54 -dependent promoters are active. Nonetheless, our results suggest that some of the genes are metabolically significant. We found that even though several purines did not support growth as the sole nitrogen source, they did stimulate growth with aspartate as the nitrogen source. Cells produced 14 CO 2 from minimal medium containing [ 14 C]adenine, which implies allantoin production. However, neither ammonia nor carbamoyl phosphate was produced, which implies that purine catabolism is incomplete and does not provide nitrogen during nitrogen-limited growth. We constructed strains with deletions of two genes whose products might catalyze the first reaction of purine catabolism. Deletion of one eliminated 14 CO 2 production from [ 14 C]adenine, which implies that its product is necessary for xanthine dehydrogenase activity. We changed the name of this gene to xdhA. The xdhA mutant grew faster with aspartate as a nitrogen source. The mutant also exhibited sensitivity to adenine, which guanosine partially reversed. Adenine sensitivity has been previously associated with defective purine salvage resulting from impaired synthesis of guanine nucleotides from adenine. We propose that xanthine dehydrogenase contributes to this purine interconversion.

Molybdenum cofactor-dependent resistance to N-hydroxylated base analogs in Escherichia coli is independent of MobA function

“…However, even the xdhA xdhD yagR triple mutation did not increase HAP sensitivity, as also reported previously [11]. The three E. coli xanthine oxidases are considered largely cryptic, although some low-level activity in a purine catabolic pathway has been described [23]. Thus, based on this survey of known and putative molybdoenzymes, the nature of the putative HAP-detoxifying activity remains still unidentified.…”

“…Among these, the crystal structure of YedY has indeed been shown the presence of MPT as cofactor, but the activity and cellular function of the protein are unclear at this time [30,37]. The three putative xanthine oxidases may play a role in purine catabolism, although their main function remains to be determined [23]. Regardless of their functions, our experiments have shown clearly that none of these MPT-bearing enzymes play a role in HAP detoxification.…”

“…The latter two have been identified as alternative DMSO reductases [29]. The database searches also identified one putative member of the sulfite oxidase family, YedY [30], one putative member of the aldehyde ferredoxin oxidoreductase family, YdhV, and three putative xanthine oxidases, XdhA, XdhD, and YagR [23].…”

“…A multiply-deficient mobA xdhA xdhD yagR ydhV yedY derivative of NR10836 was constructed as follows. First, the xdhD::miniTn10cam derivative of NR10836 was made ΔxdhA::kan by P1 transduction using as donor strain K4633-ΔxdhA::kan obtained from L. Reitzer [23]. The kan r marker was eliminated from this strain using plasmid pCP20 [20], which induces induction of recombination between the repeats flanking the kan gene.…”

Comparative phenotypic analysis and genome sequence of Clostridium beijerinckii SA-1, an offspring of NCIMB 8052

“…In SA-1, the SNV changed a histidine residue, positively charged, for a polar uncharged asparagine residue. This missense mutation at residue 47 (H47N) occurred in a conserved region of the protein and may have an effect on the function of the protein in regulating purine utilization (Xi et al, 2000;Heluane et al, 2011).…”