A surprising range of modified-methionyl S-adenosylmethionine analogues support bacterial growth

S-Adenosyl-l-methionine (AdoMet) is an essential metabolite, serving in a very wide variety of metabolic reactions. The enzyme that produces AdoMet from l-methionine and ATP (methionine adenosyltransferase, MAT) is thus an attractive target for antimicrobial agents. We previously showed that a variety of methionine analogues are MAT substrates, yielding AdoMet analogues that function in specific methyltransfer reactions. However, this left open the question of whether the modified AdoMet molecules could support bacterial growth, meaning that they functioned in the full range of essential AdoMet-dependent reactions. The answer matters both for insight into the functional flexibility of key metabolic enzymes, and for drug design strategies for both MAT inhibitors and selectively toxic MAT substrates. In this study, methionine analogues were converted in vitro into AdoMet analogues, and tested with an Escherichia coli strain lacking MAT (ΔmetK) but that produces a heterologous AdoMet transporter. Growth that yields viable, morphologically normal cells provides exceptionally robust evidence that the analogue functions in every essential reaction in which AdoMet participates. Overall, the S-adenosylated derivatives of all tested l-methionine analogues modified at the carboxyl moiety, and some others as well, showed in vivo functionality sufficient to allow good growth in both rich and minimal media, with high viability and morphological normality. As the analogues were chosen based on incompatibility with the reactions via which AdoMet is used to produce acylhomoserine lactones (AHLs) for quorum sensing, these results support the possibility of using this route to selectively interfere with AHL biosynthesis without inhibiting bacterial growth.