3.A.1.7.3
High-affinity phosphate-specific permease, PstAB/PhoS. The 3-d structure of PhoS = (PBP) = PfluDING) has been solved at high resolution by x-ray crystallography (Ahn et al. 2007) with phosphate bound (4F1U and 4F1V; 0.95Å resolution) and with arsenate bound (4F18 and 4F19; 0.88Å resolution) (Elias et al. 2012). Phosphate binds with 500-fold higher affinity than arsenate due to a dense and rigid network of ion-dipole interactions (Elias et al. 2012). The PBP from Halomonas sp. GFAJ-1 has a phosphate affinity 5000-fold higher than that of arsenate (Elias et al. 2012).