Protocol to quantify polyphosphate in human cell lines using a tagged PPBD peptide.

Polyphosphate (polyP) is an evolutionarily conserved polymer of phosphates that is difficult to study in human cells because of its low concentration and high lability. First, we described how to express and purify Xpress-tagged PPBD (Ppx1 PolyP Binding Domain). We describe the detection and quantification of nuclear polyP in HEK293T cells using Xpress-PPBD, Xpress antibody, and Alexa-conjugated secondary antibodies. We have also used this protocol in SH-SY5Y HeLa and HEK293 cells. For complete details on the use and execution of this protocol, please refer to Samper-Martín et al. (2021).

Polyphosphate degradation by Nudt3-Zn2+ mediates oxidative stress response.

Polyphosphate (polyP) is a polymer of hundreds of phosphate residues present in all organisms. In mammals, polyP is involved in crucial physiological processes, including coagulation, inflammation, and stress response. However, after decades of research, the metabolic enzymes are still unknown. Here, we purify and identify Nudt3, a NUDIX family member, as the enzyme responsible for polyP phosphatase activity in mammalian cells. We show that Nudt3 shifts its substrate specificity depending on the cation; specifically, Nudt3 is active on polyP when Zn2+ is present. Nudt3 has in vivo polyP phosphatase activity in human cells, and importantly, we show that cells with altered polyP levels by modifying Nudt3 protein amount present reduced viability upon oxidative stress and increased DNA damage, suggesting that polyP and Nudt3 play a role in oxidative stress protection. Finally, we show that Nudt3 is involved in the early stages of embryo development in zebrafish.