A pentose bisphosphate pathway of nucleotide degradation in Promethearchaeum syntrophicum.

Asgard archaea are a group of archaea found in various natural environments such as deep-sea sediments and mangrove wetlands, garnering significant attention for the presence of eukaryotic signature proteins and close phylogenetic links to the origin of eukaryotes. However, as most Asgard archaea have not yet been successfully cultured, research into their biological characteristics and metabolic mechanisms remains in its early stages, primarily relying on genomic data obtained from environmental samples. Here, we report that the classical pentose bisphosphate pathway of nucleoside degradation is also widely distributed in Asgard archaea. This pathway, which links nucleotide recycling to central carbon metabolism, has been proposed as a relic of ancient heterotrophy, with its ribose moiety representing one of the first abundant fermentable sugars available to early heterotrophs. To functionally validate this pathway, we conducted a biochemical examination of the three key enzymes involved in this pathway-nucleoside-5'-monophosphate phosphorylase, ribose-1,5-bisphosphate isomerase, and ribulose-1,5-bisphosphate carboxylase/oxygenase-from Promethearchaeum syntrophicum MK-D1, the first cultured representative of Asgard archaea. Our results strongly suggest that these enzymes play a role in the conversion of nucleoside monophosphates to 3-phosphoglycerate in P. syntrophicum. These findings provide new experimental insights into the metabolism and physiology of Asgard archaea.