Characterization of a Novel WDR5-binding Site That Recruits RbBP5 through a Conserved Motif to Enhance Methylation of Histone H3 Lysine 4 by Mixed Lineage Leukemia Protein-1*

Zain Odho,Stacey M Southall,Jon R Wilson

doi:10.1074/jbc.m110.159921

Zain Odho, Stacey M Southall + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m110.159921

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Abstract

Histone modification is well established as a fundamental mechanism driving the regulation of transcription, replication, and DNA repair through the control of chromatin structure. Likewise, it is apparent that incorrect targeting of histone modifications contributes to misregulated gene expression and hence to developmental disorders and diseases of genomic instability such as cancer. The KMT2 family of SET domain methyltransferases, typified by mixed lineage leukemia protein-1 (MLL1), is responsible for histone H3 lysine 4 methylation, a marker of active genes. To ensure that this modification is correctly targeted, a multiprotein complex associates with the methyltransferase and directs activity. We have identified a novel interaction site on the core complex protein WD repeat protein-5 (WDR5), and we mapped the complementary site on its partner retinoblastoma-binding protein-5 (RbBP5). We have characterized this interaction by x-ray crystallography and show how it is fundamental to the assembly of the complex and to the regulation of methyltransferase activity. We show which region of RbBP5 contributes directly to mixed lineage leukemia activation, and we combine our structural and biochemical data to produce a model to show how WDR5 and RbBP5 act cooperatively to stimulate activity.

Highlights

Create and maintain the correct gene transcription profiles and to facilitate the appropriate response to environmental stimulation, it is essential that the enzymes that deposit or remove these marks be accurately targeted and their activity tightly regulated
We present a new analysis of the WD repeat protein-5 (WDR5)/retinoblastoma-binding protein-5 (RbBP5) interaction that reveals a novel binding site on the opposite face of the WDR5 ␤-propeller from that shown to interact with histone H3 or mixed lineage leukemia protein-1 (MLL1)
Enhancement of Methyltransferase Activity by WDR5 and RbBP5—It is well established that WDR5, a conserved protein of the KMT2 core complex, is essential for the MLL1 enzyme to achieve its full methyltransferase activity [21, 25]

Summary

The abbreviations used are

H3K4, histone H3 lysine 4; MLL, mixed-lineage leukemia; BisTris, 2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol; Ni-NTA, nickel-nitrilotriacetic acid. This motif is located in an apparently unstructured region just outside the N-flanking regions of the catalytic SET domain, and it binds in the same way to the axial cavity of WDR5 as described for the H3 peptide Disruption of this interaction is detrimental to the assembly and overall methylation activity of the complex [27, 29]. In the crystal structure of the MLL1 SET domain in complex with a histone tail peptide, the substrate peptide is buried deep in a cleft in the protein making it difficult to envisage a mechanism where the H3 lysine is presented to the catalytic site by WDR5. We map the interaction to a conserved motif in RbBP5 and describe the role of the different regions of RbBP5 in the stimulation of methyltransferase activity and combine structural and biochemical data to develop a model for the tripartite complex between the two ␤-propeller proteins and MLL1

EXPERIMENTAL PROCEDURES

RESULTS

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