RESUMO
Rhodoquinone (RQ) is a close analogue of ubiquinone (UQ) that confers diverse bacterial and eukaryotic taxa the ability to utilize fumarate as an electron acceptor in hypoxic conditions. The RquA protein, identified in a Rhodospirillum rubrum RQ-deficient mutant, has been shown to be required for RQ biosynthesis in bacteria. In this report, we demonstrate that RquA, homologous to SAM-dependent methyltransferases, is necessary and sufficient to catalyze RQ biosynthesis from UQ in vitro. Remarkably, we show that RquA uses SAM as the amino group donor in a substitution reaction that converts UQ to RQ. In contrast to known aminotransferases, RquA does not use pyridoxal 5'-phosphate (PLP) as a coenzyme, but requires the presence of Mn2+ as a cofactor. As these findings reveal, RquA provides an example of a non-canonical SAM-dependent enzyme that does not catalyze methyl transfer, instead it uses SAM in an atypical amino transfer mechanism.
RESUMO
Estes and Aziz are mycobacteriophages that were isolated on Mycolicibacterium smegmatis mc2155 at room temperature from soil samples collected in Spokane, WA. Their genome sequences are 83,601 and 83,412 bp long, respectively, and they are members of subcluster M2. Each contains 21 tRNA genes and short conserved repeats characteristic of cluster M phages.
