An Active C-Terminally Truncated Form of Ca²⁺/Calmodulin-Dependent Protein Kinase Phosphatase-N (CaMKP-N/PPM1E)

Abstract

Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP/PPM1F) and its nuclear homolog CaMKP-N (PPM1E) are Ser/Thr protein phosphatases that belong to the PPM family. CaMKP-N is expressed in the brain and undergoes proteolytic processing to yield a C-terminally truncated form. The physiological significance of this processing, however, is not fully understood. Using a wheat-embryo cell-free protein expression system, we prepared human CaMKP-N (hCaMKP-N(WT)) and the truncated form, hCaMKP-N(1–559), to compare their enzymatic properties using a phosphopeptide substrate. The hCaMKP-N(1–559) exhibited a much higher V max value than the hCaMKP-N(WT) did, suggesting that the processing may be a regulatory mechanism to generate a more active species. The active form, hCaMKP-N(1–559), showed Mn2+ or Mg2+-dependent phosphatase activity with a strong preference for phospho-Thr residues and was severely inhibited by NaF, but not by okadaic acid, calyculin A, or 1-amino-8-naphthol-2,4-disulfonic acid, a specific inhibitor of CaMKP. It could bind to postsynaptic density and dephosphorylate the autophosphorylated Ca2+/calmodulin-dependent protein kinase II. Furthermore, it was inactivated by H2O2 treatment, and the inactivation was completely reversed by treatment with DTT, implying that this process is reversibly regulated by oxidation/reduction. The truncated CaMKP-N may play an important physiological role in neuronal cells.

Highly expressed genes within hippocampal sector CA1: implications for the physiology of memory

“…PPM1E appears to be a protein phosphatase that specifically dephosphorylates and regulates multifunctional calcium and Calmodulin-regulated kinases but unique in that it localizes the nucleus (hence, -N). Ishida et al 20 found that by using gene knockdown studies in zebrafish, they were able to conclude that this enzyme was essential for the early development of the brain and spinal cord. As the pattern of expression for PPM1E was fairly intense and specific for CA1, further research on the functional role this enzyme may play in hippocampal physiology overall with specific inquiry to any possible role in memory formation.…”

The role of POPX2 in the regulation of hippo pathway

“…A study conducted by Ishida et. al with a C-terminally truncated version of POPX1 (1-559) found that the proteolytic processed version of POPX1 exhibit higher phosphatase activity compared to the full length, suggesting that the proteolytic processing of POPX1 at the C-terminal serves as a post-translational regulatory mechanism to generate a highly active phosphatase (Ishida et al, 2013). The PP2C phosphatase domain in grey.…”