Disease Association and Druggability of WD40 Repeat Proteins

WD40 repeat (WDR) domains are protein interaction scaffolds that represent one of the largest protein families in human, and a first WDR inhibitoran allosteric antagonist of polycomb repressive complex 2just entered the clinic. A systematic analysis of the CORUM database of protein complexes shows that WDR is the most represented domain in transcriptional regulation and one of the most prevalent in the ubiquitin proteasome system, two pathways of high relevance to drug discovery. Parsing the literature and the vulnerability of cancer cell lines to CRISPR knockout indicates that WDR proteins are targets of interest in oncology and other disease areas. A quantitative analysis of WDR structures reveals that druggable binding pockets can be found on multiple surfaces of these multifaceted protein interaction platforms. These data support the development of chemical probes to further interrogate WDR proteins as an emerging therapeutic target class

An Integrative Proteomic Approach Identifies Novel Cellular SMYD2 Substrates

Protein methylation is a post-translational modification with important roles in transcriptional regulation and other biological processes, but the enzyme–substrate relationship between the 68 known human protein methyltransferases and the thousands of reported methylation sites is poorly understood. Here, we propose a bioinformatic approach that integrates structural, biochemical, cellular, and proteomic data to identify novel cellular substrates of the lysine methyltransferase SMYD2. Of the 14 novel putative SMYD2 substrates identified by our approach, six were confirmed in cells by immunoprecipitation: MAPT, CCAR2, EEF2, NCOA3, STUB1, and UTP14A. Treatment with the selective SMYD2 inhibitor BAY-598 abrogated the methylation signal, indicating that methylation of these novel substrates was dependent on the catalytic activity of the enzyme. We believe that our integrative approach can be applied to other protein lysine methyltransferases, and help understand how lysine methylation participates in wider signaling processes

An Integrative Proteomic Approach Identifies Novel Cellular SMYD2 Substrates

Protein methylation is a post-translational modification with important roles in transcriptional regulation and other biological processes, but the enzyme–substrate relationship between the 68 known human protein methyltransferases and the thousands of reported methylation sites is poorly understood. Here, we propose a bioinformatic approach that integrates structural, biochemical, cellular, and proteomic data to identify novel cellular substrates of the lysine methyltransferase SMYD2. Of the 14 novel putative SMYD2 substrates identified by our approach, six were confirmed in cells by immunoprecipitation: MAPT, CCAR2, EEF2, NCOA3, STUB1, and UTP14A. Treatment with the selective SMYD2 inhibitor BAY-598 abrogated the methylation signal, indicating that methylation of these novel substrates was dependent on the catalytic activity of the enzyme. We believe that our integrative approach can be applied to other protein lysine methyltransferases, and help understand how lysine methylation participates in wider signaling processes

Strategy to Target the Substrate Binding site of SET Domain Protein Methyltransferases

Protein methyltransferases (PMTs) are a novel gene family of therapeutic relevance involved in chromatin-mediated signaling and other biological mechanisms. Most PMTs are organized around the structurally conserved SET domain that catalyzes the methylation of a substrate lysine. A few potent chemical inhibitors compete with the protein substrate, and all are anchored in the channel recruiting the methyl-accepting lysine. We propose a novel strategy to design focused chemical libraries targeting the substrate binding site, where a limited number of warheads each occupying the lysine-channel of multiple enzymes would be decorated by different substituents. A variety of sequence and structure-based approaches used to analyze the diversity of the lysine channel of SET domain PMTs support the relevance of this strategy. We show that chemical fragments derived from published inhibitors are valid warheads that can be used in the design of novel focused libraries targeting other PMTs

Identification and Structure–Activity Relationship of HDAC6 Zinc-Finger Ubiquitin Binding Domain Inhibitors

HDAC6 plays a central role in the recruitment of protein aggregates for lysosomal degradation and is a promising target for combination therapy with proteasome inhibitors in multiple myeloma. Pharmacologically displacing ubiquitin from the zinc-finger ubiquitin-binding domain (ZnF-UBD) of HDAC6 is an underexplored alternative to catalytic inhibition. Here, we present the discovery of an HDAC6 ZnF-UBD-focused chemical series and its progression from virtual screening hits to low micromolar inhibitors. A carboxylate mimicking the C-terminal extremity of ubiquitin, and an extended aromatic system stacking with W1182 and R1155, are necessary for activity. One of the compounds induced a conformational remodeling of the binding site where the primary binding pocket opens up onto a ligand-able secondary pocket that may be exploited to increase potency. The preliminary structure–activity relationship accompanied by nine crystal structures should enable further optimization into a chemical probe to investigate the merit of targeting the ZnF-UBD of HDAC6 in multiple myeloma and other diseases

Identification and Structure–Activity Relationship of HDAC6 Zinc-Finger Ubiquitin Binding Domain Inhibitors

HDAC6 plays a central role in the recruitment of protein aggregates for lysosomal degradation and is a promising target for combination therapy with proteasome inhibitors in multiple myeloma. Pharmacologically displacing ubiquitin from the zinc-finger ubiquitin-binding domain (ZnF-UBD) of HDAC6 is an underexplored alternative to catalytic inhibition. Here, we present the discovery of an HDAC6 ZnF-UBD-focused chemical series and its progression from virtual screening hits to low micromolar inhibitors. A carboxylate mimicking the C-terminal extremity of ubiquitin, and an extended aromatic system stacking with W1182 and R1155, are necessary for activity. One of the compounds induced a conformational remodeling of the binding site where the primary binding pocket opens up onto a ligand-able secondary pocket that may be exploited to increase potency. The preliminary structure–activity relationship accompanied by nine crystal structures should enable further optimization into a chemical probe to investigate the merit of targeting the ZnF-UBD of HDAC6 in multiple myeloma and other diseases

Identification and Structure–Activity Relationship of HDAC6 Zinc-Finger Ubiquitin Binding Domain Inhibitors

HDAC6 plays a central role in the recruitment of protein aggregates for lysosomal degradation and is a promising target for combination therapy with proteasome inhibitors in multiple myeloma. Pharmacologically displacing ubiquitin from the zinc-finger ubiquitin-binding domain (ZnF-UBD) of HDAC6 is an underexplored alternative to catalytic inhibition. Here, we present the discovery of an HDAC6 ZnF-UBD-focused chemical series and its progression from virtual screening hits to low micromolar inhibitors. A carboxylate mimicking the C-terminal extremity of ubiquitin, and an extended aromatic system stacking with W1182 and R1155, are necessary for activity. One of the compounds induced a conformational remodeling of the binding site where the primary binding pocket opens up onto a ligand-able secondary pocket that may be exploited to increase potency. The preliminary structure–activity relationship accompanied by nine crystal structures should enable further optimization into a chemical probe to investigate the merit of targeting the ZnF-UBD of HDAC6 in multiple myeloma and other diseases

Structure of the Catalytic Domain of EZH2 Reveals Conformational Plasticity in Cofactor and Substrate Binding Sites and Explains Oncogenic Mutations

<div><p>Polycomb repressive complex 2 (PRC2) is an important regulator of cellular differentiation and cell type identity. Overexpression or activating mutations of EZH2, the catalytic component of the PRC2 complex, are linked to hyper-trimethylation of lysine 27 of histone H3 (H3K27me3) in many cancers. Potent EZH2 inhibitors that reduce levels of H3K27me3 kill mutant lymphoma cells and are efficacious in a mouse xenograft model of malignant rhabdoid tumors. Unlike most SET domain methyltransferases, EZH2 requires PRC2 components, SUZ12 and EED, for activity, but the mechanism by which catalysis is promoted in the PRC2 complex is unknown. We solved the 2.0 Å crystal structure of the EZH2 methyltransferase domain revealing that most of the canonical structural features of SET domain methyltransferase structures are conserved. The site of methyl transfer is in a catalytically competent state, and the structure clarifies the structural mechanism underlying oncogenic hyper-trimethylation of H3K27 in tumors harboring mutations at Y641 or A677. On the other hand, the I-SET and post-SET domains occupy atypical positions relative to the core SET domain resulting in incomplete formation of the cofactor binding site and occlusion of the substrate binding groove. A novel CXC domain N-terminal to the SET domain may contribute to the apparent inactive conformation. We propose that protein interactions within the PRC2 complex modulate the trajectory of the post-SET and I-SET domains of EZH2 in favor of a catalytically competent conformation.</p> </div

The cofactor binding site of EZH2 is incomplete.

<p>(A) Superimposition of the EZH2 structure (colored mesh; post-SET shown as blue ribbon) with a ternary complex of EHMT1/GLP (white ribbon) shows that the cofactor binding site is only partially formed in EZH2, due to an atypical orientation of the post-SET domain. (B) The cofactor site of EZH2 is occupied by the CXC domain of a second molecule within the crystal lattice. (C) Mapping of the location of lysine-mediated cross-links detected in the purified PRC2 complex [53]. Cross-links between Lys735 and Lys569 as well as Lys713 indicate that the post-SET domain of EZH2 (yellow) can project towards the CXC domain in solution, consistent with the conformation seen in our structure.</p

Catalytic activity and substrate/cofactor binding of EZH2 (520-746) and the trimeric (EZH2-EED-SUZ12) complex.

<p>(A) The full-length trimeric complex (●) was active, and the crystallized EZH2 construct (○) was not. Activity assay conditions were optimized for the full length EZH2 in complex with EED and SUZ12 as a control. Kinetic analysis shows that the trimeric complex binds SAM (B) and a histone peptide (C) (K_m SAM: 900 ± 100 nM; K_m peptide: 205 ± 25 nM; k_cat: 24 ± 2 h^-1). Apparent kinetic parameters are the average of three measurements ± standard deviation. ITC shows that the crystallized construct binds neither SAM (D) nor the peptide substrate (E). </p