Role of Aggregatibacter actinomycetemcomitans in glutathione catabolism

Introduction: Our previous studies demonstrated that three enzymes, γ-glutamyltransferase (GGT), cysteinylglycinase (CGase) and cystalysin, are required for the catabolism of glutathione to produce hydrogen sulfide (H ₂S) in Treponema denticola. In this study, we examined glutathione catabolism in Aggregatibacter actinomycetemcomitans. Methods: The GGT and CGase of A. actinomycetemcomitans were determined by biological methods and GGT was characterized using a molecular biological approach. Results: A. actinomycetemcomitans showed GGT and CGase activity, but could not produce H ₂S from glutathione. The addition of recombinant T. denticola cystalysin, an l-cysteine desulfhydrase, to whole cells of A. actinomycetemcomitans resulted in the production of H ₂S from glutathione. Subsequently, we cloned A. actinomycetemcomitans GGT gene (ggt) and overexpressed the 63 kDa GGT protein. The recombinant A. actinomycetemcomitans GGT was purified and identified. The K _cat/K _m of the recombinant GGT from N-γ-l-glutamyl-4-nitroaniline as substrate was 31/μm/min. The activity of GGT was optimum at pH 6.9-7.1 and enhanced by thiol-containing compounds. Conclusion: The results demonstrated that A. actinomycetemcomitans had GGT and CGase activities and that the GGT was characterized. The possible role of A. actinomycetemcomitans in glutathione metabolism and H ₂S production from oral bacteria was discussed.