Polyphosphate attachment to lysine repeats is a non-covalent protein modification

Abstract

Polyphosphate (polyP) is a chain of inorganic phosphate that is present in all domains of life and affects diverse cellular phenomena, ranging from blood clotting to cancer. A study by Azevedo etal. described a protein modification whereby polyP is attached to lysine residues within polyacidic serine and lysine (PASK) motifs via what the authors claimed to be covalent phosphoramidate bonding. This was based largely on the remarkable ability of the modification to survive extreme denaturing conditions. Our study demonstrates that lysine polyphosphorylation is non-covalent, based on its sensitivity to ionic strength and lysine protonation and absence of phosphoramidate bond formation, as analyzed via 31P NMR. Ionic interaction with lysine residues alone is sufficient for polyP modification, and we present a new list of non-PASK lysine repeat proteins that undergo polyP modification. This work clarifies the biochemistry of polyP-lysine modification, with important implications for both studying and modulating this phenomenon. This Matters Arising paper is in response to Azevedo etal. (2015), published in Molecular Cell. See also the Matters Arising Response by Azevedo etal. (2024), published in this issue.