Structural studies of new post-translational modification erasers/readers

Abstract

Structural studies of new post-translational modification erasers/readers Quan Hao School of Biomedical Sciences, University of Hong Kong, Hong Kong Email: qhao@hku.hk Sirtuins are NAD–dependent deacetylases that regulate important biological processes. Four mammalian sirtuins (Sirt4 to Sirt7) have no detectable or very weak deacetylase activity. Using structural and biochemical data we have discovered that Sirt5 is an efficient desuccinylase and demalonylase in vitro and in vivo, catalyzing the hydrolysis of succinyl and malonyl lysine residues. Sirt5 is the first Sirtuin demonstrated to prefer an acyl group other than acetyl, suggesting that other Sirtuins showing little or no deacetylation activity may prefer to hydrolyze different acyl groups too [1]. We have further demonstrated that Sirt6 catalyzes the removal of long chain fatty acyl groups. Sirt6 promotes the secretion of tumor necrosis factor-α (TNFα) by removing the fatty acyl modification on this cytokine. The crystal structure of Sirt6 with a myristoyl peptide may pave a way for novel therapeutic interventions in the field of autoimmunity and inflammation [2]. We have also shown that Sirt3 is a decrotonylase in vitro and in cells. The crystal structure of Sirt3-H3K4Cr complex reveals a unique binding pocket that stabilizes the conjugated crotonyl group via  stacking [3]. Using potent SIRT2-specific inhibitors, we have recently captured a distinct covalent catalytic intermediate (III) that is different from the previously established intermediates I and II; MALDI-TOF data further support the intermediate III formation [4]. This is the first time such an intermediate has been captured by X-ray crystallography and provides more mechanistic insights into sirtuin-catalyzed reactions. Our recent biochemical and structural studies have demonstrated that GAS41, an oncogene-coded protein, can act as the reader of succinylation on histone H3K122. This is the first time that a reader of succinyl-lysine (Ksuc) on histones has been identified [5]. This work is support by Hong Kong RGC grants C7037-14G and AoE/P-705/16. [1] Du et al, Science, Vol. 334, 806-809 (2011). [2] Jiang et al, Nature, 496, 110–113 (2013). [3] Bao et al, eLife, 3:e02999 (2014). [4] Wang et al, Cell Chem. Biol. 24 (3), 339-345 (2017). [5] Wang et al, PNAS, 115 (10), 2365-2370 (2018).