The subunits of the nonspecific lethal (NSL) complex, which include the histone acetyltransferase MOF (males absent on the first), play important roles in various cellular functions, including transcription regulation and stem cell identity maintenance and reprogramming, and are frequently misregulated in disease. Here, we provide the first biochemical and structural insights into the molecular architecture of this large multiprotein assembly. We identified several direct interactions within the complex and show that KANSL1 acts as a scaffold protein interacting with four other subunits, including WDR5, which in turn binds KANSL2. Structural analysis of the KANSL1/WDR5/KANSL2 subcomplex reveals how WDR5 is recruited into the NSL complex via conserved linear motifs of KANSL1 and KANSL2. Using structure-based KANSL1 mutants in transgenic flies, we show that the KANSL1-WDR5 interaction is required for proper assembly, efficient recruitment of the NSL complex to target promoters, and fly viability. Our data clearly show that the interactions of WDR5 with the MOF-containing NSL complex and MLL/COMPASS histone methyltransferase complexes are mutually exclusive. We propose that rather than being a shared subunit, WDR5 plays an important role in assembling distinct histone-modifying complexes with different epigenetic regulatory roles.

The human macrophage galactose‐type lectin (MGL), expressed on macrophages and dendritic cells (DCs), modulates distinct immune cell responses by recognizing N‐acetylgalactosamine (GalNAc) containing structures present on pathogens, self‐glycoproteins, and tumor cells. Herein, NMR spectroscopy and molecular dynamics (MD) simulations were used to investigate the structural preferences of MGL against different GalNAc‐containing structures derived from the blood group A antigen, the Forssman antigen, and the GM2 glycolipid. NMR spectroscopic analysis of the MGL carbohydrate recognition domain (MGL‐CRD, C181‐H316) in the absence and presence of methyl α‐GalNAc (α‐MeGalNAc), a simple monosaccharide, shows that the MGL‐CRD is highly dynamic and its structure is strongly altered upon ligand binding. This plasticity of the MGL‐CRD structure explains the ability of MGL to accommodate different GalNAc‐containing molecules. However, key differences are observed in the recognition process depending on whether the GalNAc is part of the blood group A antigen, the Forssman antigen, or GM2‐derived structures. These results are in accordance with molecular dynamics simulations that suggest the existence of a distinct MGL binding mechanism depending on the context of GalNAc moiety presentation. These results afford new perspectives for the rational design of GalNAc modifications that fine tune MGL immune responses in distinct biological contexts, especially in malignancy.