Study of duplicated galU genes in Rhodococcus jostii and a putative new metabolic node for glucosamine-1P in...

Studying enzymes that determine glucose-1P fate in carbohydrate metabolism is important to better understand microorganisms as biotechnological tools. One example ripe for discovery is the UDP-glucose pyrophosphorylase enzyme from Rhodococcus spp. In the R. jostii genome, this gene is duplicated, whereas R. fascians contains only one copy.

We report the molecular cloning of galU genes from R. jostii and R. fascians to produce recombinant proteins RjoGalU1, RjoGalU2, and RfaGalU. Substrate saturation curves were conducted, kinetic parameters were obtained and the catalytic efficiency (k_cat/K_m) was used to analyze enzyme promiscuity. We also investigated the response of R. jostii GlmU pyrophosphorylase activity with different sugar-1Ps, which may compete for substrates with RjoGalU2.

All enzymes were active as pyrophosphorylases and exhibited substrate promiscuity toward sugar-1Ps. Remarkably, RjoGalU2 exhibited one order of magnitude higher activity with glucosamine-1P than glucose-1P, the canonical substrate. Glucosamine-1P activity was also significant in RfaGalU. The efficient use of the phospho-amino-sugar suggests the feasibility of the reaction to occur in vivo. Also, RjoGalU2 and RfaGalU represent enzymatic tools for the production of (amino)glucosyl precursors for the putative synthesis of novel molecules.

Results support the hypothesis that partitioning of glucosamine-1P includes an uncharacterized metabolic node in Rhodococcus spp., which could be important for producing diverse alternatives for carbohydrate metabolism in biotechnological applications.

Results presented here provide a model to study evolutionary enzyme promiscuity, which could be used as a tool to expand an organism's metabolic repertoire by incorporating non-canonical substrates into novel metabolic pathways.