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Activation and Inhibition of Histone Deacetylase 8 by Monovalent Cations
Authors:Stephanie L. Gantt   Caleb G. Joseph     Carol A. Fierke
Affiliation:From the Departments of Chemistry, ;§Medicinal Chemistry, and ;Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055
Abstract:The metal-dependent histone deacetylases (HDACs) catalyze hydrolysis of acetyl groups from acetyllysine side chains and are targets of cancer therapeutics. Two bound monovalent cations (MVCs) of unknown function have been previously observed in crystal structures of HDAC8; site 1 is near the active site, whereas site 2 is located >20 Å from the catalytic metal ion. Here we demonstrate that one bound MVC activates catalytic activity (K1/2 = 3.4 mm for K+), whereas the second, weaker-binding MVC (K1/2 = 26 mm for K+) decreases catalytic activity by 11-fold. The weaker binding MVC also enhances the affinity of the HDAC inhibitor suberoylanilide hydroxamic acid by 5-fold. The site 1 MVC is coordinated by the side chain of Asp-176 that also forms a hydrogen bond with His-142, one of two histidines important for catalytic activity. The D176A and H142A mutants each increase the K1/2 for potassium inhibition by ≥40-fold, demonstrating that the inhibitory cation binds to site 1. Furthermore, the MVC inhibition is mediated by His-142, suggesting that this residue is protonated for maximal HDAC8 activity. Therefore, His-142 functions either as an electrostatic catalyst or a general acid. The activating MVC binds in the distal site and causes a time-dependent increase in activity, suggesting that the site 2 MVC stabilizes an active conformation of the enzyme. Sodium binds more weakly to both sites and activates HDAC8 to a lesser extent than potassium. Therefore, it is likely that potassium is the predominant MVC bound to HDAC8 in vivo.
Keywords:Enzymes/Catalysis   Enzymes/Hydrolases   Enzymes/Mechanisms   Enzymes/Metallo   Histones/Deacetylase   Protein/Post-translational Modification   Inhibition   Monovalent Cation
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