Comparative genomics and functional analysis of the NiaP family uncover nicotinate transporters from bacteria, plants, and mammals

Abstract

The transporter(s) that mediate uptake of nicotinate and its N-methyl derivative trigonelline are not known in plants, and certain mammalian nicotinate transporters also remain unidentified. Potential candidates for these missing transporters include proteins from the ubiquitous NiaP family. In bacteria, niaP genes often belong to NAD-related regulons, and genetic evidence supports a role for Bacillus subtilis and Acinetobacter baumannii NiaP proteins in uptake of nicotinate or nicotinamide. Other bacterial niaP genes are, however, not in NAD-related regulons but cluster on the chromosome with choline-related (e.g., Ralstonia solanacearum and Burkholderia xenovorans) or thiamin-related (e.g., Thermus thermophilus) genes, implying that they might encode transporters for these compounds. Radiometric uptake assays using Lactococcus lactis cells expressing NiaP proteins showed that B. subtilis, R. solanacearum, and B. xenovorans NiaP transport nicotinate via an energy-dependent mechanism. Likewise, NiaP proteins from maize (GRMZM2G381453, GRMZM2G066801, and GRMZM2G081774), Arabidopsis (At3g13050), and mouse (SVOP) transported nicotinate; the Arabidopsis protein also transported trigonelline. In contrast, T. thermophilus NiaP transported only thiamin. None of the proteins tested transported choline or the thiazole and pyrimidine products of thiamin breakdown. The maize and Arabidopsis NiaP proteins are the first nicotinate transporters reported in plants, the Arabidopsis protein is the first trigonelline transporter, and mouse SVOP appears to represent a novel type of mammalian nicotinate transporter. More generally, these results indicate that specificity for nicotinate is conserved widely, but not absolutely, among pro- and eukaryotic NiaP family proteins.

Comparative Genomics of Cultured and Uncultured Strains Suggests Genes Essential for Free-Living Growth of Liberibacter

“…However, L. crescens has a niacin/H+ symporter (NiaP) not found in the other two Liberibacter genomes. NiaP in Ralstonia solanacearum transports nicotinate and is energy dependent [18]. The L. crescens NiaP sequence is most similar to those in A. tumefaciens and other Rhizobiaceae .…”

Does Abiotic Stress Cause Functional B Vitamin Deficiency in Plants?

“…Arabidopsis NiaP also transports trigonelline (Fig. 4) (Jeanguenin et al, 2012). NiaP is probably located in the plasma membrane (Jeanguenin et al, 2012), suggesting that nicotinate salvaged in one location could be reused for NAD(P) + synthesis in another.…”

“…4) (Jeanguenin et al, 2012). NiaP is probably located in the plasma membrane (Jeanguenin et al, 2012), suggesting that nicotinate salvaged in one location could be reused for NAD(P) + synthesis in another. This would be consistent with the classical evidence for inter-organ exchange of nicotinate (Bonner and Bonner, 1948).…”

Essential role of Bordetella NadC in a quinolinate salvage pathway for NAD biosynthesis

“…The classical Bordetellae, B. avium, B. hinzii, B. pseudohinzii and B. trematum have both the pncA and pncB genes needed for a pyridine salvage pathway to produce NaMN from exogenously supplied Nm and Na respectively. However, B. avium, B. trematum, B. ansorpii and B. petrii have genes encoding proteins similar to NiaP, a major facilitator protein for niacin uptake (Jeanguenin et al, 2012). NaMN, at the convergence of both the de novo and salvage pathways, is converted to nicotinic acid adenine dinucleotide (NaAD) via the predicted nicotinic acid mononucleotide adenylyltransferase (NadD) (Hughes et al, 1983;Mehl et al, 2000) present in all examined Bordetella species.…”