Acetylation facilitates NPM1 anchoring in the nucleolus by boosting liquid-liquid phase separation

Abstract

Nucleophosmin (NPM1) is a multifunctional nucleolar protein whose integration into the nucleolus relies on multivalent interactions that drive liquid-liquid phase separation (LLPS). Acetylation of Lys27 and Lys54 within the N-terminal oligomerization domain of NPM1 has been implicated in its nucleolar redistribution during the DNA damage response, but the molecular mechanisms underlying this redistribution remain unclear. Here, we show that Lys27/Lys54 acetylation facilitates NPM1 anchoring in the nucleolus under basal conditions by promoting LLPS. Despite preserving NPM1 structural integrity and oligomerization equilibrium, lysine acetylation reshapes the electrostatic surface potential of the N-terminal domain, neutralizing a predominantly basic region and exposing a previously cryptic acidic surface. This increased charge blockiness enhances the ability of NPM1 to undergo both homotypic and heterotypic LLPS. Thus, lysine acetylation acts as a modulator of NPM1 interaction landscape, promoting its integration into nucleolar condensates despite not constituting the primary determinant of its localization.