Protein STM3547 From Salmonella typhimurium Is a Phosphofructose Kinase B‐Type Enzyme With Ribose Kinase Activity

The first step in the metabolic utilization of ribose is the phosphorylation of its 5′ hydroxyl group. The enteropathogenic bacterium Salmonella enterica subsp. enterica sv. Typhimurium str. LT2 (hereafter S. Typhimurium) has two known enzymes that can phosphorylate D‐ribose, namely ribose kinase (RbsK) and deoxyribose kinase (DeoK). Here, we report in vivo and in vitro evidence to support the conclusion that the previously uncharacterized STM3547 protein of this bacterium has ribose kinase activity, and we propose naming it RikA (Ribokinase A). Our bioinformatics analyses show end‐to‐end sequence identity/similarity among RikA, RbsK, and DeoK, and site‐directed mutagenesis of RikA showed that, like in RbsK and DeoK, an aspartate residue (position 343 in RikA) is critical for enzymatic activity. We found that RikA has K m values comparable to those of RbsK and DeoK for both ribose and ATP, and that all three proteins display cooperative binding of ATP induced by ribose. Together, these data suggest that the ribose‐induced conformational changes observed in E. coli RbsK also occur in all three ribose kinases of S. typhimurium . Notably, while RikA has robust ribose kinase activity, it can only poorly phosphorylate 2‐deoxy‐D‐ribose, D‐xylose, and D‐xylulose, and it cannot phosphorylate L‐arabinose. Collectively, our data support the conclusion that the RikA protein is a member of the phosphofructose kinase B‐type (PfkB) family of sugar kinases.