Identification of a 5′-deoxyadenosine deaminase in Methanocaldococcus jannaschii and its possible role in recycling the radical s-adenosylmethionine enzyme reaction product 5′-deoxyadenosine

Abstract

We characterize here the MJ1541 gene product from Methanocaldococcus jannaschii, an enzyme that was annotated as a 5'-methylthioadenosine/S-adenosylhomocysteine deaminase (EC 3.5.4.31/3.5.4.28). The MJ1541 gene product catalyzes the conversion of 5'-deoxyadenosine to 5′-deoxyinosine as its major product but will also deaminate 5'-methylthioadenosine, S-adenosylhomocysteine, and adenosine to a small extent. On the basis of these findings, we are naming this new enzyme 5′-deoxyadenosine deaminase (DadD). The Km for 5'-deoxyadenosine was found to be 14.0±1.2 μM with a kcat/Km of 9.1×109 M-1 s-1. Radical S-adenosylmethionine (SAM) enzymes account for nearly 2% of the M. jannaschii genome, where the major SAM derived products is 5′-deoxyadenosine. Since 5′-dA has been demonstrated to be an inhibitor of radical SAM enzymes; a pathway for removing this product must be present. We propose here that DadD is involved in the recycling of 5′-deoxyadenosine, whereupon the 5'-deoxyribose moiety of 5'-deoxyinosine is further metabolized to deoxyhexoses used for the biosynthesis of aromatic amino acids in methanogens. © 2014, American Society for Microbiology.