This region has been named the SPX domain after (Syg1, Pho81 and XPR1). The domain is found at the amino terminus of a variety of proteins. The N-termini of several proteins involved in the regulation of phosphate transport, including the putative phosphate level sensors Pho81 from Saccharomyces cerevisiae and NUC-2 from Neurospora crassa, are also members of this family. The yeast protein Gde1/Ypl110c is similar to both, NUC-2 and Pho81, in sharing their multi-domain architecture, which includes the SPX N-terminal domain followed by several ankyrin repeats and a C-terminal glycerophosphodiester phosphodiesterase domain (GDPD). Gde1 hydrolyzes intracellular glycerophosphocholine into glycerolphosphate and choline, and plays a role in the utilization of glycerophosphocholine as a source for phosphate.
Jiyao W et al.(2023). "The conserved domain database in 2023.",