Table 1.

List of available crystal structures for NPF/POT transporters.

Protein	Organism	ExxER motif	TMH4–TMH10 Salt bridge	TMH1–TMH7 Salt bridge	Conformation	Ligand	PDB ID	Reference
AtNPF6.3	Arabidopsis thaliana	EAVER	Yes	No	Inward-open Inward-open Inward-open	None Nitrate Nitrate	5A2N 5A2O 4OH3	Parker and Newstead, 2014 Sun et al., 2014
PepTSo	Shewanella oneidensis	EACER	Yes	Yes	Occluded state Inward-open	None None	2XUT 4UVM	Newstead et al., 2011 Fowler et al., 2015
PepTSo2	Shewanella oneidensis	ELWER	Yes	No	Inward-open Inward-open Inward-open Inward-open	Alafosfalin Ala-Ala-Ala Ala-Tyr-(Br) Ala-Tyr-(Br)-Ala	4LEP 4TPJ 4TPH 4TPG	Guettou et al., 2013 Guettou et al., 2014
PepTSt	Streptococcus thermophilus	EMWER	Yes	Yes	Inward-open Inward-open Inward-open	None None None	4APS 4D2B 5MMT	Solcan et al., 2012 Lyons et al., 2014 Quistgaard et al., 2017
GkPOT	Geobacillus kaustophilus	EFWER	Yes	No	Inward-open Inward-open	None Alafosfalin	4IKV 4IKZ	Doki et al., 2013
YbgH	Escherichia coli	QIWEY	Yes	No	Inward-open	None	4Q65	Zhao et al., 2014
YePEPT	Yersinia enterocolitica	EMWER	Yes	Yes	Inward-open	None	4W6V	Boggavarapu et al., 2015
PepTXc	Xanthomonas campestris	EACER	Yes	Yes	Auto-inhibited	None	6EI3	Parker et al., 2017

The sole crystal structure of an NPF transporter, NPF6.3 from A. thaliana was obtained by two different groups and solved as an apo-protein or in the presence of nitrate. The crystal structures of seven POT proteins from six different bacteria were solved as apo-proteins, in complex with the peptide mimic alafosfalin or with di- or tri-peptides. Protein Data Bank Identification Codes (PDB ID) for each solved structure are included.