The role of N-terminal acetylation on biomolecular condensation.

N-terminal acetylation (Nt-acetylation) is one of the most prevalent co-translational modifications in eukaryotes, affecting nearly 80% of the human proteome. Despite its ubiquity, the potential impact of this phenomenon on biomolecular condensation has been largely overlooked. Here, we uncover how this chemically subtle modification can exert broad and multifaceted control over phase behaviour, using Grh1, a Golgi-associated protein involved in stress-induced secretion in yeast, as a model system. We show that Nt-acetylation reshapes protein partitioning and condensate formation, reduces droplet size and number, dampens pH sensitivity, weakens electrostatic contributions, and suppresses water dipolar relaxation within condensates, indicating reduced internal hydration and environmental responsiveness. These effects are accompanied by acetylation-dependent dimerisation and local structural changes, including a concentration-dependent gain in α-helicity. Remarkably, co-condensation assays reveal that acetylated and non-acetylated forms of the same protein are only partially miscible, giving rise to core-shell architectures driven by differences in interfacial tension. Together, our findings highlight Nt-acetylation as a potent, generalisable regulator of condensate material properties, linking primary sequence chemistry to mesoscale organisation. Given its evolutionary conservation and prevalence across eukaryotic proteomes, Nt-acetylation may represent a widespread mechanism for modulating protein condensation in health and disease.