A Novel Mechanism for SIRT1 Activators That Does Not Rely on the Chemical Moiety Immediately C-Terminal to the Acetyl-Lysine of the Substrate.

SIRT1, an NAD-dependent deacetylase, catalyzes the deacetylation of proteins coupled with the breakdown of NAD into nicotinamide and 2'-O-acetyl-ADP-ribose (OAADPr). Selective SIRT1 activators have potential clinical applications in atherosclerosis, acute renal injury, and Alzheimer's disease. Here, we found that the activity of the potent SIRT1 activator CWR is independent of the acetylated substrate. It adopts a novel mechanism to promote SIRT1 activity by covalently bonding to the anomeric C1' carbon of the ribose ring in OAADPr. In addition, CWR is highly selective for SIRT1, with no effect on SIRT2, SIRT3, SIRT5, or SIRT6. The longer distance between the anomeric C1' carbon of the ribose ring in OAADPr and Arg274 of SIRT1 (a conserved residue among sirtuins) than that between the anomeric C1' carbon in OAADPr and the Arg of SIRT2, SIRT3, SIRT5, and SIRT6, should be responsible for the high selectivity of CWR for SIRT1. This was confirmed by site-directed mutagenesis of SIRT3. Consistent with the in vitro assays, the activator also reduced the acetylation levels of p53 in a concentration-dependent manner via SIRT1 in cells. Our study provides a new perspective for designing SIRT1 activators that does not rely on the chemical moiety immediately C-terminal to the acetyl-lysine of the substrate.