6qxz
Solution structure of the ASHH2 CW domain with the N-terminal histone H3 tail mimicking peptide monomethylated on lysine 4
Structural highlights
FunctionASHH2_ARATH Histone methyltransferase involved in di and tri-methylation of 'Lys-36' of histone H3 (H3K36me2 and H3K36me3). Binds to H3 already mono- or di-methylated on 'Lys-4'(H3K4me1 or H3K4me2), but not to H3K4me3. H3K4me and H3K36me represent specific tags for epigenetic transcriptional activation. Regulates positively FLC transcription to prevent early flowering transition. Required for flowering transition in response to vernalization and for the maintenance of FLC expression in late embryos, but dispensable for the initial reactivation in early embryos during reprogramming. Seems also to modulate several traits including floral organ size, root size and dormancy. Promotes apical dominance (PubMed:16299497, PubMed:10518493, PubMed:16258034, PubMed:18070919, PubMed:19915673, PubMed:20711170). Directly involved in the tri-methylation of 'Lys-36' of histone H3 (H3K36me3) at LAZ5 chromatin to maintain a transcriptionally active state of LAZ5, a TIR-NB-LRR protein involved in innate immunity (PubMed:20949080).[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedChromatin post-translational modifications are thought to be important for epigenetic effects on gene expression. Methylation of histone N-terminal tail lysine residues constitutes one of many such modifications, executed by families of histone lysine methyltransferase (HKMTase). One such protein is ASHH2 from the flowering plant Arabidopsis thaliana, equipped with the interaction domain, CW, and the HKMTase domain, SET. The CW domain of ASHH2 is a selective binder of monomethylation at lysine 4 on histone H3 (H3K4me1) and likely helps the enzyme dock correctly onto chromatin sites. The study of CW and related interaction domains has so far been emphasizing lock-key models, missing important aspects of histone-tail CW interactions. We here present an analysis of the ASHH2 CW-H3K4me1 complex using NMR and molecular dynamics, as well as mutation and affinity studies of flexible coils. beta-augmentation and rearrangement of coils coincide with changes in the flexibility of the complex, in particular the eta1, eta3 and C-terminal coils, but also in the beta1 and beta2 strands and the C-terminal part of the ligand. Furthermore, we show that mutating residues with outlier dynamic behaviour affect the complex binding affinity despite these not being in direct contact with the ligand. Overall, the binding process is consistent with conformational selection. We propose that this binding mechanism presents an advantage when searching for the correct post-translational modification state among the highly modified and flexible histone tails, and also that the binding shifts the catalytic SET domain towards the nucleosome. DATABASES: Structural data are available in the PDB database under the accession code 6QXZ. Resonance assignments for CW42 in its apo- and holo-forms are available in the BMRB database under the accession code 27251. The Arabidopsis (ASHH2) CW domain binds monomethylated K4 of the histone H3 tail through conformational selection.,Dobrovolska O, Brilkov M, Madeleine N, Odegard-Fougner O, Stromland O, Martin SR, De Marco V, Christodoulou E, Teigen K, Isaksson J, Underhaug J, Reuter N, Aalen RB, Aasland R, Halskau O FEBS J. 2020 Oct;287(20):4458-4480. doi: 10.1111/febs.15256. Epub 2020 Mar 24. PMID:32083791[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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