Abstract 1536 Sirtuins as dual function writer and eraser enzymes

Sirtuins are NAD+-dependent deacetylases of which there are 7 family member in humans (SIRT1-7). Canonically, SIRT1-2 are nucleocytoplasmic, SIRT3-5 are mitochondrial, and SIRT6-7 are nuclear. Collectively, these enzymes play key roles across a wide variety of cellular functions by controlling the acetylation status of proteins. Sirtuins have also been reported to remove acyl groups larger than acetyl (e.g., propionyl, succinyl, myristoyl etc.) as well. Interestingly, sirtuins exhibit mono-ADP-ribosyltransferase (MARylase) function as well, conferring a "writer" role in addition to their canonical "eraser" role. We investigated the deacylation and ADP-ribosyltransferase activities of SIRT6 in biochemical and cell-based assays. We found that SIRT6 readily delactylates histones within chromatin even though it is a poor delactylase toward peptide substrates. We further found that SIRT6 and class I HDACs operate independently (versus being redundant) in controlling chromatin lactylation, suggesting distinct regulatory roles for these deacetylases. On the MARylation front, our biochemical studies have revealed surprising details about how SIRT6 is activated toward MARylation, what amino acid SIRT6 modifies, and what proteins SIRT6 MARylates. This mechanistic information will inform our ongoing efforts to investigate SIRT6 MARylation in cells to better understand this aspect of SIRT6. Altogether, this work is helping us to better understand this busy enzyme and its family members. We acknowledge the National Institutes of Health R35GM143080 and P30CA042014 and the University of Utah Research Foundation for funding.