Summary Mitochondrial sirtuins, SIRT3-5, are NAD+-dependent deacylases and ADP-ribosyltransferases critical for stress responses. However, a comprehensive understanding of sirtuin targets, regulation of sirtuin activity, and the relationships between sirtuins remains a key challenge in mitochondrial physiology. Here, we employ systematic interaction proteomics to elucidate the mitochondrial sirtuin protein interaction landscape. This work reveals sirtuin interactions with numerous functional modules within mitochondria, identifies candidate sirtuin substrates, and uncovers a fundamental role for sequestration of SIRT3 by ATP synthase in mitochondrial homeostasis. In healthy mitochondria, a pool of SIRT3 binds ATP synthase, but upon matrix pH reduction with concomitant loss of mitochondrial membrane potential, SIRT3 dissociates. This release correlates with rapid deacetylation of matrix proteins and SIRT3 is required for recovery of membrane potential. In vitro reconstitution experiments, as well as Crispr/Cas9 engineered cells, indicate that pH-dependent SIRT3 release requires H135 in ATP5O. Our SIRT3-5 interaction network provides a framework for discovering novel biological functions regulated by mitochondrial sirtuins.

Highlights d PDAC regional heterogeneity stems from sub-tumor microenvironments (subTMEs) d SubTMEs exhibit distinct immune phenotypes and CAF differentiation states d SubTMEs execute distinct tumor-promoting and chemoprotective functions d Intratumoral subTME co-occurrence links stromal heterogeneity to patient outcome

S 2020, 'GATA6 expression distinguishes classical and basal-like subtypes in advanced pancreatic cancer. ', Clinical Cancer Research.