The interaction of human sirtuins with isoliquiritigenin

Abstract

Sirtuins are a class of NAD+-dependent deacetylase, catalyzing the removal of acyl group modifications from lysine. Deacylation regulates a wide range of the biological activities such as cell proliferation, insulin secretion, fatty acid metabolism, and lifespan extension. Modulators of sirtuins are potential therapeutics for cancers, diabetes, and aging. Isoliquiritigenin is a polyphenol discovered in licorice which possesses SIRT1 activation effects. The structure of isoliquiritigenin is similar to resveratrol, which has been known as a phenolic chemical activator of SIRT1 and known as a cancer alleviator via promoting calorie restriction. It was proved that Isoliquiritigenin has many basic pharmacological effects such as tumor suppression, anti-inflammatory, anti-oxidative and anti-diabetic effect, indicating its potential for clinical and pharmaceutic application. However, the mechanism of how isoliquiritigenin interacts with SIRT1 and whether isoliquiritigenin interacts with other sirtuins have not been well studied. In this research, I have expressed and purified six of the seven human sirtuin proteins except for SIRT4. The NAD+ cycling assay was performed to investigate how isoliquiritigenin impacts sirtuin’s activity and the kinetic factor of human SIRT2 deacetylation was obtained. Results of the cycling assay were presented in this thesis, demonstrating the discrepancy of the sirtuin activation effect at different concentrations of isoliquiritigenin. In my results, SIRT1 showed the modest effect in isoliquiritigenin activation, SIRT2 and SIRT6 presented largely increased deacylation activity with the presence of isoliquiritigenin, while SIRT3 and SIRT5 do not respond to isoliquiritigenin activation. The specificity constant of the deacetylation of SIRT2 with or without isoliquiritigenin was calculated and compared for further study of the catalytic efficiency of SIRT2 in presence of isoliquiritigenin. This research could be a starting point for the mechanism investigation on how isoliquiritigenin interacts with sirtuins, which will be a benefit for anti-diabetes drug development, such as optimization of small molecule activators.