The intrinsically disordered protein NUPR1 binds to phospholipids

The nuclear protein 1 (NUPR1) is an intrinsically disordered protein (IDP) involved in stress-mediated cellular conditions, with an interactome including many other partner proteins, as well as nucleic acids. We wondered whether its great conformational flexibility and biological versatility could include interactions with lipids. Binding between NUPR1 and phosphatidylserine (PS) and phosphatidylinositol biphosphate (PIP2) was verified in cellulo by using proximity ligation assay (PLA) techniques in MiaPaCa-2 cells. Binding in vitro was assayed against PS, and against PS in a mixture with phosphatidylcholine (PC), and it was confirmed by using nuclear magnetic resonance (NMR) and biolayer interferometry (BLI). Furthermore, results in silico also showed the association between NUPR1 and the lipids, occurring in a mostly aspecific way on the membrane surface, but with a slight preference for the binding through the protein hot-spot regions: the most common interaction sites with other molecular species: around Ala33 and Thr68. All together, these techniques unambiguously indicate that NUPR1 was bound to lipids. We discuss the potential biological consequences of our findings, including the possible relevance of NUPR1 in participating in the stability of membrane organelles, as well as in modulating cellular signaling.