Crystal structures of human SIRT3 displaying substrate-induced conformational changes

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Sirtuin 3 (SIRT3) is a mitochondrial deacetylase crucial for metabolism and energy production.
• SIRT3 is implicated in the health benefits of exercise and caloric restriction.
• It is a potential therapeutic target for metabolic and neurological disorders.

Purpose of the Study:

• To determine the first crystal structures of human SIRT3.
• To elucidate the structural mechanisms of SIRT3 substrate binding and deacetylation activity.
• To understand the role of substrate and cofactor binding in SIRT3 conformational changes.

Main Methods:

• X-ray crystallography was used to obtain structures of human SIRT3 in various states: apo, with acetylated substrate peptide, as a reaction intermediate, and with dethioacetylated peptide.
• Isothermal titration calorimetry (ITC) was employed to study substrate binding kinetics.

Main Results:

• The study presents the first crystal structures of human SIRT3, including apo, substrate-bound, intermediate, and product-bound states.
• Structural analysis reveals conformational changes induced by the binding of the acetylated substrate peptide and NAD(+).
• ITC data indicate that the acetylated peptide binds to SIRT3 before NAD(+).

Conclusions:

• The determined structures provide critical insights into the mechanism of SIRT3-mediated deacetylation.
• Understanding substrate and cofactor interactions is key to comprehending SIRT3's functional regulation.
• These findings lay the groundwork for developing SIRT3-targeted therapeutics for metabolic and neurological diseases.