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The hydroxylation activity of Jmjd6 is required for its homo‐oligomerization

Jumonji C‐terminal (JmjC) domain‐containing proteins are protein hydroxylases and histone demethylases that control gene expression. Jumonji domain‐containing protein 6 (Jmjd6) is indispensable for embryonic development and has both histone arginine demethylase and lysyl‐hydroxylase activities. The protein undergoes post‐translational homo‐oligomerization, but the underlying mechanism remains unknown. In this study, we examined the enzymatic activity of Jmjd6 and uncovered the mechanism underlying its homo‐oligomerization. An in vitro enzymatic assay monitored by matrix‐assisted laser desorption‐ionization time‐of‐flight (MALDI‐TOF) mass spectrometry indicates that Jmjd6 is unable to remove the methyl group from histone arginine residues but can hydroxylate the histone H4 tail at lysine residues in a 2‐oxoglutarate (2‐OG)‐ and Fe (II)‐dependent manner. A mutational analysis reveals that the homo‐oligomerization of Jmjd6 requires its enzymatic activity and the N‐ and C‐termini. Using an in vitro enzymatic assay, we further demonstrate that Jmjd6 can hydroxylate its N‐terminus but not its C‐terminus. In summary, we did not detect arginine demethylase activity for Jmjd6, but we did confirm that it could catalyze the lysyl‐hydroxylation of histone peptides. In addition, we demonstrated that the homo‐oligomerization of Jmjd6 requires its own enzymatic activity and the N‐ and C‐termini. We propose that Jmjd6 forms intermolecular covalent bonds between its N‐ and C‐termini via autohydroxylation. J. Cell. Biochem. 113: 1663–1670, 2012. © 2011 Wiley Periodicals, Inc.