Putative glycerophosphodiester phosphodiesterase domain of ankyrin repeat protein NUC-2 and similar proteins
This subfamily corresponds to a putative glycerophosphodiester phosphodiesterase domain (GDPD) present in Neurospora crassa ankyrin repeat protein NUC-2 and its Saccharomyces cerevisiae counterpart, Phosphate system positive regulatory protein PHO81. Some uncharacterized NUC-2 sequence homologs are also included in this family. NUC-2 plays an important role in the phosphate-regulated signal transduction pathway in Neurospora crassa. It shows high similarity to a cyclin-dependent kinase inhibitory protein PHO81, which is part of the phosphate regulatory cascade in S. cerevisiae. Both NUC-2 and PHO81 have multi-domain architecture, including an SPX N-terminal domain following by several ankyrin repeats and a putative C-terminal GDPD domain with unknown function. Although the putative GDPD domain displays sequence homology to that of bacterial glycerophosphodiester phosphodiesterases (GP-GDEs, EC 22.214.171.124), the residues essential for interactions with the substrates and calcium ions in bacterial GP-GDEs are not conserved in members of this family, which suggests the function of putative GDPD domains in these proteins might be distinct from those in typical bacterial GP-GDEs.