Factors Determining Sirtuin-1 Target Engagement.

Sirtuin-1 (Sirt1) is a key NAD+-dependent deacylase regulating metabolism, stress responses, genome stability, and aging. Although well-characterized biochemically and structurally, its substrate selectivity remains unclear: in vitro, Sirt1 appears promiscuous, while in vivo it activates particular processes in response to different stimuli. Emerging evidence indicates that selectivity arises from multiple regulatory layers beyond the catalytic site. Here we review how post-translational modifications (PTMs) ‒ including phosphorylation, acetylation, and glycosylation ‒ modulate activity, localization, and substrate affinity. For instance, phosphorylation at S27/T530 (by JNK1) or S682 (by HIPK2) affects nuclear translocation, substrate targeting, or complex formation with cofactors such as AROS and DBC1. Protein-protein interactions, for example with DBC1, PACS2, and transcription factors, further direct Sirt1 to specific substrates or compartments, functioning as allosteric regulators. Spatial compartmentalization, including nucleocytoplasmic shuttling and localization to promyelocytic leukemia nuclear bodies (PML-NBs), integrates Sirt1 into defined signaling contexts. Moreover, liquid-liquid phase separation (LLPS) may concentrate Sirt1 and substrates within condensates, enhancing its selectivity. Overall, Sirt1 specificity emerges from PTMs, interactions, localization, and phase behavior ‒ offering a framework for developing selective modulators in metabolic and age-related diseases.