The conservation of phosphate-binding residues among PHT1 transporters suggests that distinct transport affinities are unlikely to result from differences in the phosphate-binding site

Abstract

The plant PHosphate Transporter 1 (PHT1) family of membrane proteins belongs to the major facilitator super family and plays a major role in the acquisition of inorganic phosphate (Pi) from the soil and its transport within the plant. These transporters have been well characterized for expression patterns, localization, and in some cases affinity. Furthermore, the crystal structure of a high-affinity eukaryotic phosphate transporter from the fungus Piriformospora indica (PiPT) has revealed important information on the residues involved in Pi transport. Using multiple-sequence alignments and homology modelling, the phosphate-binding site residues were shown to be well conserved between all the plant PHT1 proteins, Saccharomyces cerevisiae PHO84 and PiPT. For example, Asp 324 in PiPT is conserved in the equivalent position in all plant PHT1 and yeast transporters analyzed, and this residue in ScPHO84 was shown by mutagenesis to be important for both the binding and transport of Pi. Moreover, Asp 45 and Asp 149, which are predicted to be involved in proton import, and Lys 459, which is putatively involved in Pi-binding, are all fully conserved in PHT1 and ScPHO84 transporters. The conserved nature of the residues that play a key role in Pi-binding and transport across the PHT1 family suggests that the differing Pi affinities of these transporters do not reside in differences in the Pi-binding site. Recent studies suggest that phosphate transporters could possess dual affinity and that post-translational modifications may be important in regulating affinity for phosphate.

Functional characterization of the PHT1 family transporters of foxtail millet with development of a novel Agrobacterium-mediated transformation procedure

“…Their functions were characterized by heterologous expression in Saccharomyces cerevisiae Pi transporter deficient mutants and Xenopus oocytes. PHT1 transporters are found to have 12 transmembrane segments and belong to the Major Facilitator Superfamily (MFS) of transporters 5 , 7 .…”

Uncoupling growth from phosphorus uptake in Lemna: Implications for use of duckweed in wastewater remediation and P recovery in temperate climates

“…Measurement of 32 P orthophosphate uptake at 22°C at a range of phosphate concentrations showed a biphasic plot consistent with low‐ and high‐affinity transport components (Figure 4b) as described previously (Ullrich‐Eberius et al., 1984). The Spirodela genome has three putative phosphate transporters of the PHT1 family which could encode the transporters responsible for this activity (Table S1, Figure S1) but it is not possible to say based on protein sequence conservation and modeling which are responsible for the different activities (Ceasar, Baker, Baker, Muench, Ignacimuthu, & Baldwin, 2016). Indeed, it has been reported that plant phosphate transporters may be able to switch between high‐ and low‐affinity modes (Ayadi et al., 2015).…”

Genome‐wide Identification and in silico Analysis of PHT1 Family Genes and Proteins in Setaria viridis: The Best Model to Study Nutrient Transport in Millets

“…2). In a previous study, it was reported that all 12 foxtail millet PHT1s have the same conserved amino acids for Pi binding and H + and Pi transport as found in PiPT (Ceasar et al, 2016). The key resides involved in Pi binding for PiPT are tyrosine 150, glutamine 177, tryphtophan 320, aspartic acid 324, tyrosine 328, and asparagine 431 (Pedersen et al, 2013).…”

“…Expression of SiPHT1;8 and SiPHT1;9 in roots was selectively induced by colonization with F. mosseae (Ceasar et al, 2014). Homology modeling was also performed for all these transporters, along with other characterized plant PHT1s (Ceasar et al, 2016), with the crystal structure of the Piriformospora indica phosphate transporter (PiPT) as a template (Pedersen et al, 2013). The phosphate‐binding site residues were found to be well conserved in SiPHT1 like in other plant PHT1 proteins such as Saccharomyces cerevisiae PHO84 phosphate transporter and PiPT.…”

“…The phosphate‐binding site residues were found to be well conserved in SiPHT1 like in other plant PHT1 proteins such as Saccharomyces cerevisiae PHO84 phosphate transporter and PiPT. The important residues involved in Pi binding, H + binding, and transport were identified; such residues (aspartic acid 324, aspartic acid 45, aspartic acid 149, and lysine 459) were shown to be well conserved in foxtail millet PHT1 proteins (Ceasar et al, 2016).…”