The plasticity of WDR5 peptide-binding cleft enables the binding of the SET1 family of histone methyltransferases

Ottawa Institute of Systems Biology, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON, Canada.
Nucleic Acids Research (Impact Factor: 9.11). 01/2012; 40(9):4237-46. DOI: 10.1093/nar/gkr1235
Source: PubMed


In mammals, the SET1 family of lysine methyltransferases (KMTs), which includes MLL1-5, SET1A and SET1B, catalyzes the methylation of lysine-4 (Lys-4) on histone H3. Recent reports have demonstrated that a three-subunit complex composed of WD-repeat protein-5 (WDR5), retinoblastoma-binding protein-5 (RbBP5) and absent, small, homeotic disks-2-like (ASH2L) stimulates the methyltransferase activity of MLL1. On the basis of studies showing that this stimulation is in part controlled by an interaction between WDR5 and a small region located in close proximity of the MLL1 catalytic domain [referred to as the WDR5-interacting motif (Win)], it has been suggested that WDR5 might play an analogous role in scaffolding the other SET1 complexes. We herein provide biochemical and structural evidence showing that WDR5 binds the Win motifs of MLL2-4, SET1A and SET1B. Comparative analysis of WDR5-Win complexes reveals that binding of the Win motifs is achieved by the plasticity of WDR5 peptidyl-arginine-binding cleft allowing the C-terminal ends of the Win motifs to be maintained in structurally divergent conformations. Consistently, enzymatic assays reveal that WDR5 plays an important role in the optimal stimulation of MLL2-4, SET1A and SET1B methyltransferase activity by the RbBP5-ASH2L heterodimer. Overall, our findings illustrate the function of WDR5 in scaffolding the SET1 family of KMTs and further emphasize on the important role of WDR5 in regulating global histone H3 Lys-4 methylation.

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    • "A fully formed MLL-WRAD complex is the optimally active configuration for all MLL methyltransferases. However, our data, together with those showing intrinsic activation of MLL3 (Zhang et al., 2012), suggest that there may be a hitherto unidentified function for TRR-like proteins utilizing monomethylation of H3K4 independent of the complex. "
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    ABSTRACT: Methylation of histone H3 lysine-4 is a hallmark of chromatin associated with active gene expression. The activity of H3K4-specific modification enzymes, in higher eukaryotes the MLL (or KMT2) family, is tightly regulated. The MLL family has six members, each with a specialized function. All contain a catalytic SET domain that associates with a core multiprotein complex for activation. These SET domains segregate into three classes that correlate with the arrangement of targeting domains that populate the rest of the protein. Here we show that, unlike MLL1, the MLL4 SET domain retains significant activity without the core complex. We also present the crystal structure of an inactive MLL4-tagged SET domain construct and describe conformational changes that account for MLL4 intrinsic activity. Finally, our structure explains how the MLL SET domains are able to add multiple methyl groups to the target lysine, despite having the sequence characteristics of a classical monomethylase. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
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    • "(See text for more detailed explanations). list of interband-specific proteins is taken from [27]–[28], [50]–[53]. (See text for more detailed explanations). "
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    • "While the residues of WDR5 that interact with MLL are well studied, the interactions of WDR5 with other MLL family members are not so well defined (16,37). The crystal structure suggests that Y191 has a role in WDR5's interactions with other MLL members (16,50). However, this is yet to be shown experimentally. "
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    ABSTRACT: MLL, the trithorax ortholog, is a well-characterized histone 3 lysine 4 methyltransferase that is crucial for proper regulation of the Hox genes during embryonic development. Chromosomal translocations, disrupting the Mll gene, lead to aggressive leukemia with poor prognosis. However, the functions of MLL in cellular processes like cell-cycle regulation are not well studied. Here we show that the MLL has a regulatory role during multiple phases of the cell cycle. RNAi-mediated knockdown reveals that MLL regulates S-phase progression and, proper segregation and cytokinesis during M phase. Using deletions and mutations, we narrow the cell-cycle regulatory role to the C subunit of MLL. Our analysis reveals that the transactivation domain and not the SET domain is important for the S-phase function of MLL. Surprisingly, disruption of MLL–WRAD interaction is sufficient to disrupt proper mitotic progression. These mitotic functions of WRAD are independent of SET domain of MLL and, therefore, define a new role of WRAD in subset of MLL functions. Finally, we address the overlapping and unique roles of the different SET family members in the cell cycle.
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