Structural and Enzymatic Plasticity of SIRT6 Deacylase Activity.

Sirtuin 6 (SIRT6) is an NAD-dependent protein deacylase that targets lysine residues in histones in the cell nucleus, where it helps maintain genome stability and links metabolism to epigenetic control. Dysregulation of SIRT6 is believed to be associated with aging and cancer, making it of pharmacological interest. In this study, we use cryogenic electron microscopy (cryo-EM) and enzymology to explore SIRT6 preference and adaptability towards different nucleosomal substrates. We have visualized a trapped complex of SIRT6 in the process of deacylating H3K27, demonstrating how SIRT6 undergoes conformational changes to remove differently positioned histone marks. Additional biochemical studies further reveal SIRT6's plasticity, which accommodates various metabolism-linked modifications such as lysine lactylation and β-hydroxybutyrylation. To further understand the basis for substrate selectivity of SIRT6, we explore the effects of an established G60A enzyme mutation, proximal H3 modifications, and small molecule modulators. These findings highlight SIRT6's versatility and provide key mechanistic insights into its molecular recognition.