The solute transport and binding profile of a novel nucleobase cation symporter 2 from the honeybee pathogen Paenibacillus larvae

Abstract

Here, we report that a novel nucleobase cation symporter 2 encoded in the genome of the honeybee bacterial pathogen Paenibacillus larvae reveals high levels of amino acid sequence similarity to the Escherichia coli and Bacillus subtilis uric acid and xanthine transporters. This transporter is named P. larvae uric acid permease‐like protein (PlUacP). Even though PlUacP displays overall amino acid sequence similarities, has common secondary structures, and shares functional motifs and functionally important amino acids with E. coli xanthine and uric acid transporters, these commonalities are insufficient to assign transport function to PlUacP. The solute transport and binding profile of PlUacP was determined by radiolabeled uptake experiments via heterologous expression in nucleobase transporter‐deficient Saccharomyces cerevisiae strains. PlUacP transports the purines adenine and guanine and the pyrimidine uracil. Hypoxanthine, xanthine, and cytosine are not transported by PlUacP, but, along with uric acid, bind in a competitive manner. PlUacP has strong affinity for adenine K m 7.04 ± 0.18 μ m , and as with other bacterial and plant NCS 2 proteins, PlUacP function is inhibited by the proton disruptor carbonyl cyanide m‐chlorophenylhydrazone. The solute transport and binding profile identifies PlUacP as a novel nucleobase transporter.

Substrate translocation in SLC23 and SLC26 transporters

“…Next to that, UapA from Aspergillus niduans has also been functionally well-characterized. Additionally, uracil uptake has been investigated in some protozoan parasites, such as Trypanosoma brucei brucei and Leishmania major, and the honey bee pathogen Paenibacillus larvae (De Koning and Jarvis, 1998;Papageorgiou et al, 2005;Gudin et al, 2006;Stoffer-Bittner et al, 2018;Campagnaro and de Koning, 2020). Protozoan parasites generally lost the ability of de novo synthesis of nucleobases and rely on the uptake from the host environment through various transport systems.…”

“…The putative binding site residues of PlUP (with the exception of F346, that is Y342 in UraA) are absolutely identical to the ones of UraA (Figure S31). The other homolog, PlUacP (NCBI reference sequence: WP_023485062.1), transports adenine, guanine and uracil and additionally binds hypoxanthine, xanthine, cytosine and uric acid (Stoffer-Bittner et al, 2018). This protein shares higher sequence similarity with the uric acid transporter UacT from E. coli (43%) than with UraA (28%).…”