Identification of a New Class of Adenosine Deaminase from Helicobacter pylori with Homologs among Diverse Taxa

Abstract

Early studies of Helicobacter pylori's nutritional requirements alluded to a complete purine salvage network in this organism. Recently, this hypothesis was confirmed in two strains of H. pylori, whose purine requirements were satisfied by any single purine base or nucleoside. Most of the purine conversion enzymes in H. pylori have been studied using mutant analysis; however, the gene encoding adenosine deaminase (ADD) in H. pylori remained unidentified. Through stepwise protein purification followed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF), we discovered that H. pylori ADD is encoded by hp0267, an apparently essential gene. Hp0267 shares no sequence homology with previously characterized ADDs, yet both are members of the amidohydrolase superfamily. Hp0267 is grouped within cog0402, while other ADDs studied to date are found in cog1816. The hp0267 locus was previously misannotated as encoding a chlorohydrolase. Using purified recombinant Hp0267, we determined the enzyme's pH optimum, temperature optimum, substrate specificity, and estimated kinetic constants. In contrast to other known ADDs, Hp0267 contains Fe(II) as the relevant metal ligand. Furthermore, Hp0267 exhibits very low deaminase activity on 2=-deoxyadenosine, a substrate that is readily hydrolyzed by cog1816 ADDs. Our preliminary comparative genomic analysis suggests that Hp0267 represents a second enzyme class of adenosine deaminase whose phyletic distribution among prokaryotes is broad.

Aminofutalosine Deaminase in the Menaquinone Pathway of Helicobacter pylori

“…Both Fe 2+ and Zn 2+ were modeled and refined on the basis of the coordination geometry and refinement parameters. The precedent of the Fe 2+ and Zn 2+ atoms was established in the original description of the closely related enzyme (Hp0267, 96% identical) from H. pylori 26695 and reported to contain both Fe 2+ and Zn 2+ by direct metal analysis and by metal substitution experiments. ,, …”

“…The precedent of the Fe 2+ and Zn 2+ atoms was established in the original description of the closely related enzyme (Hp0267, 96% identical) from H. pylori 26695 and reported to contain both Fe 2+ and Zn 2+ by direct metal analysis and by metal substitution experiments. 22,39,42 Most adenosine deaminases (both eukaryotes and prokaryotes) use Zn 2+ as the metal cofactor. 43−45 The metal content of HpAFLDA was quantified for both Fe 2+ and Zn 2+ content (Supporting Information).…”

“…This heterogeneous Fe 2+ and Zn 2+ content for HpAFLDA was similar to that found for the adenosine deaminase from Hp0267. 22 Fe 2+ -or Zn 2+ -bound only enzymes were prepared for kinetic comparison in metal removal and replacement experiments (Supporting Information). The k cat for AFL with fully Fe 2+ -substituted HpAFLDA is roughly 40% faster than that for fully Zn 2+ -substituted HpAFLDA.…”

“…21 Previously, we reported an MTA deaminase in Pseudomonas aeruginosa that catalyzes the deamination of both adenosine and MTA. 21 Interestingly, a previous study reported an adenosine deaminase capable of catalyzing SAH deamination in H. pylori strain 26695, 22 leading to the question of whether deamination of MTA/AFL also takes place in H. pylori.…”

A drought‐responsive rice amidohydrolase is the elusive plant guanine deaminase with the potential to modulate the epigenome

“…Additionally, the substrate demand for adenosine to make more IMP will tip the balance favoring the production of xanthosine and xanthine, compensating for the lack of guanine conversion to xanthine in the KO. These are logical assumptions because cases of deaminases differentiating between closely related nucleosides such as adenosine and 2 0 -deoxyadenosine are known (Miller and Maier, 2013) but the existence and utilization of 2 0deoxyadenosine for deamination remains to be shown. No gene or gene product for 2 0 -deoxyadenosine deaminase is characterized in plants to the best of our knowledge.…”