Symposium 13: Epigenetic Control of Gene

LifeSciences Collaborative Access Team, Northwestern University Center forSynchrotron Research, Argonne, IL, USA.SET domain lysine methyltransferases (KMTs) are S-adenosylmethionine(AdoMet)-dependent enzymes that catalyze the site-specific methylation of ly-sine residues in histones, transcription factors, chromatin modifying enzymes,andother proteinsubstrates. Thesemodifications mediateprotein:protein inter-actions with signaling factors that possess effector modules which can recog-nize methyllysines in a sequence-dependent manner. In addition to their sitespecificity, SET domain KMTs exhibit product specificity, which is definedas theirabilityto catalyzedifferentdegrees of methylationof thelysineepsilonamine group, thus imparting an additional hierarchy in methyllysine signaling.To understand the mechanism underlying the product specificity of SET do-main KMTs, we have structurally and functionally characterized two activesite mutants of the human monomethylase SET7/9 that alter its specificity toa dimethylase and a trimethylase, respectively. Structures of the SET7/9 mu-tantsincomplexwithpeptidesbearingunmodified,mono,di,andtrimethylatedlysines reveal that water molecules within the active site function as molecularplace holders that align the lysine epsilon amine group in a linear geometrywith the sulfonium methyl group of AdoMet to promote methyltransfer. Asthe methylation state of the lysine substrate increases during successive meth-yltransferreactions,thewatermoleculesdissociatefromtheactivesite,therebyenlargingthelysinebindingchanneltoaccommodatetheincreasingbulkofthemultiply methylated epsilon amine group. Taken together, our findings illumi-nate the catalytic roles of active site water molecules in facilitating lysine mul-tiple methylation by SET domain KMTs.2171-SympStructural Insights into the Histone Specificity of PHD FingersTatiana Kutateladze.Univ Colorado Denver, Aurora, CO, USA.Histone tails are essential components of the chromatin remodeling and genetranscription machinery. They undergo various posttranslational modifications(PTMs), including methylation at Lys and Arg residues, acetylation and ubiq-uitination at Lys residues and phosphorylation at Ser and Thr residues, andserve as docking sites for protein effectors. The histone marks can be addedor removed by histone modifying enzymes, and a few protein domains havebeen identified to specifically recognize (or read) the tail modifications. ThezincbindingPHD(planthomeodomain)fingerisarecentadditiontothefamilyof epigenetic readers. Here, we characterize binding specificity of the PHD fin-ger family using a set of biochemical, crystallographic and spectroscopic ap-proaches. We compare the crystal structures and the histone binding mecha-nisms of the PHD fingers which select for histone H3 trimethylated at lysine4 (H3K4me3) and unmodified H3. Our results provide novel insights into themolecular mechanisms underlying the biological activity of the PHD fingersand further our understanding of how the histone marks are read.Supported by NIH (CA113472 and GM071424 to TGK).2172-SympChromatin Marks: Histone-Binding Modules and Catalytic MechanismsJohn Denu.Univ Wisconsin Madison, Madison, WI, USA.No Abstract.2173-SympEpigenetic Link Between DNA Methylation and Histone ModificationsXiaodong Cheng.Emory Univ, Atlanta, GA, USA.ThemethylationofmammalianDNA,primarilyatCpGdinucleotides,haslongbeen recognized to play a major role in controlling gene expression and in co-ordinationwiththeparallelchromatin-markingsystemthatoperatesatthelevelof histone modification. I will describe recent studies on, and discusses the re-sulting biochemical and structural insights into, the DNA nucleotide methyl-transferases(Dnmts)andhistonelysinemethyltransferases(HKMTs)thatmod-ulate DNA methylation.