Glucosamine-6P and glucosamine-1P, respectively an activator and a substrate of rhodococcal ADP-glucose pyrophosphorylases, show a hint to ascertain (actino)bacterial glucosamine metabolism

Rhodococcus spp. are important microorganisms for biotechnological purposes, such as bioremediation and biofuel production. The latter, founded on the oleaginous characteristic (high lipid accumulation) exhibited by many Rhodococcus species when grown in certain carbon sources under low nitrogen availability. These bacteria accumulate glycogen during exponential growth, and the glucan plays a role as an intermediary metabolite for temporary carbon storage related to lipid metabolism. The kinetic and regulatory properties of the ADP-glucose pyrophosphorylase (ADP-GlcPPase) from Rhodococcus jostii supports this hypothesis. The enzyme was found able to use glucosamine-1P as an alternative substrate. Curiously, the activity with glucosamine-1P was sensitive to glucose-6P, the main activator of actinobacterial ADP-GlcPPases. Herein, we report the study of glucosamine-1P related to the activity and regulation of ADP-GlcPPases from R. jostii and R. fascians, with the finding that glucosamine-6P is also a significant activator. Glucosamine-6P, belonging to a node between carbon and nitrogen metabolism, was identified as a main regulator in Actinobacteria. Thus, its effect on rhodococcal ADP-GlcPPases reinforces the function proposed for glycogen as temporary carbon storage. Results indicate that the activity of the studied enzymes using glucosamine-1P as a substrate responds to the activation by several metabolites that improve their catalytic performance, which strongly suggest metabolic feasibility. Then, studying the allosteric regulation exerted on an alternative activity would open two scenarios for consideration: (i) the existence of new molecules/metabolites yet undescribed, and (ii) evolutionary mechanisms underlying enzyme promiscuity that give rise new metabolic features in bacteria.