An Insulin-Responsive Sensor in the SIRT1 Disordered Region Binds DBC1 and PACS-2 to Control Enzyme Activity

Abstract

Summary Current models of SIRT1 enzymatic regulation primarily consider the effects of fluctuating levels of its co-substrate NAD+, which binds to the stably-folded catalytic domain. By contrast, the roles of the sizeable disordered N- and C-terminal regions of SIRT1 are largely unexplored. Here, we identify an insulin-responsive sensor in the SIRT1 N-terminal region (NTR), comprising an acidic cluster (AC) and a 3-helix bundle (3HB), controlling deacetylase activity. The allosteric assistor DBC1 removes a distal N-terminal shield from the 3HB, permitting PACS-2 to engage the AC and the transiently exposed helix 3 of the 3HB, disrupting its structure and inhibiting catalysis. The SIRT1 activator (STAC) SRT1720 binds and stabilizes the 3HB, protecting SIRT1 from inhibition by PACS-2. Identification of the SIRT1 insulin-responsive sensor and its engagement by the DBC1/PACS-2 regulatory hub provides important insight into the roles of disordered regions in enzyme regulation and the mode by which STACs promote metabolic fitness.

Spatiotemporal gating of SIRT1 functions by O-GlcNAcylation is essential for liver metabolic switching and prevents hyperglycemia

“…Modifications on IDRs have been thought to differentially modulate protein-protein interactions (38) and it should be noted that the specificity domain in SIRT1 (encoded by exon-2) is part of the N-terminal IDR (34,36). In this context, the results presented here, along with literature precedence (34), indicate that metabolite-driven modification of the exon-2 domain acts to regulate the functions of this master transcriptional regulator.…”

“…S2A). Although other putative sites were also predicted to be glycosylated, we focused on characterizing the modification at the N-terminal T 160 /S 161 residues, as the exon-2 domain that harbors these residues confers binding specificities of SIRT1 to various TFs (34,36). Moreover, this region is intrinsically disordered and raises the intriguing possibility of a PTM-based mechanism of regulating such proteinprotein interactions (35,36).…”

“…Specifically, we found a regulatory PTM on SIRT1 (i.e., glycosylation), which determines interactions with its target transcription factors/ coregulators. Several studies have identified positive and negative regulators of SIRT1, including proteins like DBC1 (36,67) and modifications, such as SUMOylation and phosphorylation (52). However, mechanistic insights into their spatial and temporal regulation of substrate selectivity of SIRT1, during any physiological state transitions, remain unknown.…”

“…While SIRT1 is known to interact with several nuclear and cytosolic factors (19,20,30), it is only recently that mechanisms, which determine specificity of interactions, have begun to be understood. In this regard, we and others have recently highlighted the importance of the N-terminal domain of SIRT1 (34)(35)(36)(37). Specifically, we have shown that a domain encoded by exon-2 in SIRT1, which forms an intrinsically disordered region (IDR), acts to tether substrate proteins and is specifically required for interaction with PGC1α, PPARα, and FOXO1 (34).…”

Metabolic implications of organelle–mitochondria communication

“…In oocytes from obese mice, genetic repression of Pacs2 decreases Ca 2+ influx into mitochondria and ROS production [158]. In Pacs2 knockout mice, liver expression of FGF21 is increased and mice are resistant to diet-induced obesity [188] (Fig 4B).…”