Coenzyme A (CoA) is a ubiquitous coenzyme involved in fundamental metabolic processes. CoA is synthesized from pantothenic acid by a pathway that is largely conserved among bacteria and eukaryotes and consists of five enzymatic steps. While higher organisms, including humans, must scavenge pantothenate from the environment, most bacteria and plants are capable of de novo pantothenate biosynthesis. In Salmonella enterica, precursors to pantothenate can be salvaged, but subsequent intermediates are not transported due to their phosphorylated state, and thus the pathway from pantothenate to CoA is considered essential. Genetic analyses identified the STM4195 gene product of Salmonella enterica serovar Typhimurium as a transporter of pantothenate precursors, ketopantoate and pantoate and, to a lesser extent, pantothenate. Further results indicated that STM4195 transports a product of CoA degradation that serves as a precursor to CoA and enters the biosynthetic pathway between PanC and CoaBC (dfp). The relevant CoA derivative is distinguishable from pantothenate, pantetheine, and pantethine and has spectral properties indicating the adenine moiety of CoA is intact. Taken together, the results presented here provide evidence of a transport mechanism for the uptake of ketopantoate, pantoate, and pantothenate and demonstrate a role for STM4195 in the salvage of a CoA derivative of unknown structure. The STM4195 gene is renamed panS to reflect participation in pantothenate salvage that was uncovered herein.
Importance: This manuscript describes a transporter for two pantothenate precursors in addition to the existence and transport of a salvageable coenzyme A (CoA) derivative. Specifically, these studies defined a function for an STM protein in S. enterica that was distinct from the annotated role and led to its designation as PanS (pantothenate salvage). The presence of a salvageable CoA derivative and a transporter for it suggests the possibility that this compound is present in the environment and may serve a role in CoA synthesis for some organisms. As such, this work raises important question about CoA salvage that can be pursued with future studies in bacteria and other organisms.
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