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Structural Insights into Lysine Multiple Methylation by SET Domain Methyltransferases, SET8-Y334F / H4-Lys20me2 / AdoHcy
[SETD8_HUMAN] Protein-lysine N-methyltransferase that monomethylates both histones and non-histone proteins. Specifically monomethylates 'Lys-20' of histone H4 (H4K20me1). H4K20me1 is enriched during mitosis and represents a specific tag for epigenetic transcriptional repression. Mainly functions in euchromatin regions, thereby playing a central role in the silencing of euchromatic genes. Required for cell proliferation, probably by contributing to the maintenance of proper higher-order structure of DNA during mitosis. Involved in chromosome condensation and proper cytokinesis. Nucleosomes are preferred as substrate compared to free histones. Mediates monomethylation of p53/TP53 at 'Lys-382', leading to repress p53/TP53-target genes.      
Publication Abstract from PubMed
SET domain protein lysine methyltransferases (PKMTs) regulate transcription and other cellular functions through site-specific methylation of histones and other substrates. PKMTs catalyze the formation of monomethylated, dimethylated, or trimethylated products, establishing an additional hierarchy with respect to methyllysine recognition in signaling. Biochemical studies of PKMTs have identified a conserved position within their active sites, the Phe/Tyr switch, that governs their respective product specificities. To elucidate the mechanism underlying this switch, we have characterized a Phe/Tyr switch mutant of the histone H4 Lys-20 (H4K20) methyltransferase SET8, which alters its specificity from a monomethyltransferase to a dimethyltransferase. The crystal structures of the SET8 Y334F mutant bound to histone H4 peptides bearing unmodified, monomethyl, and dimethyl Lys-20 reveal that the phenylalanine substitution attenuates hydrogen bonding to a structurally conserved water molecule adjacent to the Phe/Tyr switch, facilitating its dissociation. The additional space generated by the solvent's dissociation enables the monomethyllysyl side chain to adopt a conformation that is catalytically competent for dimethylation and furnishes sufficient volume to accommodate the dimethyl epsilon-ammonium product. Collectively, these results indicate that the Phe/Tyr switch regulates product specificity through altering the affinity of an active-site water molecule whose dissociation is required for lysine multiple methylation.
Structural origins for the product specificity of SET domain protein methyltransferases.,Couture JF, Dirk LM, Brunzelle JS, Houtz RL, Trievel RC Proc Natl Acad Sci U S A. 2008 Dec 30;105(52):20659-64. Epub 2008 Dec 16. PMID:19088188
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.