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bioRxiv · 10.1101/2022.04.04.486905

Multistate structures of the MLL1-WRAD complex bound to H2B-ubiquitinated nucleosome

Hoffmann, N.·Rahman, S.·Worden, E. J.·Smith, M. L.·Namitz, K. E.·Knutson, B.·Cosgrove, M. S.·Wolberger, C.
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Abstract

The human Mixed Lineage Leukemia-1 (MLL1) complex orchestrates methylation of histone H3K4 to promote transcription and is stimulated by monoubiquitination of histone H2B. Recent structures of the MLL1-WRAD core complex, which comprises the MLL1 methyltransferase, WDR5, RbBp5, Ash2L, and DPY-30, have revealed variation in the docking of MLL1-WRAD on nucleosomes and left ambiguous portions of Ash2L and the position of DPY30. We used an integrated approach combining cryo-electron microscopy and mass spectrometry-crosslinking to determine structures of the MLL1-WRAD complex bound to ubiquitinated nucleosomes containing the Ash2L intrinsically disordered region (IDR), SPRY insertion region, Sdc1-DPY30 interacting region (SDI-motif), and the DPY30 dimer. We resolved three additional states of MLL1-WRAD lacking one or more subunits, which may reflect different steps in the assembly of MLL1-WRAD. The subunits in all four states are positioned on the nucleosome in manner that is similar to a previous structure of MLL1-WRAD bound to ubiquitinated nucleosome, but that differs from structures with unmodified nucleosomes, suggesting that H2B-ubiquitin favors assembly of the active complex. Our results provide a more complete picture of MLL1-WRAD and the role of ubiquitin in promoting formation of the active methyltransferase complex. SignificanceThe Mixed Lineage Leukemia-1 (MLL1) complex plays a role in activating transcription by methylating lysine 4 in histone H3, a reaction that is stimulated by the presence of ubiquitin conjugated to histone H2B. Recent structures of the core MLL1 complex, termed MLL1-WRAD, have revealed the existence of multiple docking states and have also left ambiguous portions of the structure. Here we combine mass spectrometry-cross linking with cryo-EM to model additional regions of the MLL1-WRAD complex and identify a series of states that light on complex assembly and the role that ubiquitin plays in orienting MLL1-WRAD on nucleosomes.

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Hoffmann, N., Rahman, S., Worden, E. J., Smith, M. L., Namitz, K. E., Knutson, B., Cosgrove, M. S., Wolberger, C.. 2022-04-04. Multistate structures of the MLL1-WRAD complex bound to H2B-ubiquitinated nucleosome. https://doi.org/10.1101/2022.04.04.486905

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