They have also served as consultants for Kura Oncology, have equity ownership in the company, and are coinventors (along with SK, TW, LS, and PR) on patent applications covering MI-3454 (PCT/US2017/022535). PR is an employee of Kura Oncology, Inc. and has a significant ownership interest in the parent of Wellspring Biosciences, Inc. FB is an employee of Kura Oncology, Inc. Kura Oncology, Inc. and the University of Michigan have filed patent applications covering MI-3454 and they hold intellectual property rights on this compound. OAW has served as a consultant for H3B Biomedicine, Foundation Medicine Inc, Merck, and Janssen, and has received prior research funding from H3B Biomedicine unrelated to the current manuscript. MG receives research support from Cellectis and serves as a consultant in SeqRx.

The assembly of individual protein subunits into large-scale symmetrical structures is widespread in nature and confers new biological properties. Engineered protein assemblies have potential applications in nanotechnology and medicine; however, a major challenge in engineering assemblies de novo has been to design interactions between the protein subunits so that they specifically assemble into the desired structure. Here we demonstrate a simple, generalizable approach to assemble proteins into cage-like structures that uses short de novo designed coiled-coil domains to mediate assembly. We assembled eight copies of a C 3 -symmetric trimeric esterase into a well-defined octahedral protein cage by appending a C 4 -symmetric coiled-coil domain to the protein through a short, flexible linker sequence, with the approximate length of the linker sequence determined by computational modeling. The structure of the cage was verified using a combination of analytical ultracentrifugation, native electrospray mass spectrometry, and negative stain and cryoelectron microscopy. For the protein cage to assemble correctly, it was necessary to optimize the length of the linker sequence. This observation suggests that flexibility between the two protein domains is important to allow the protein subunits sufficient freedom to assemble into the geometry specified by the combination of C 4 and C 3 symmetry elements. Because this approach is inherently modular and places minimal requirements on the structural features of the protein building blocks, it could be extended to assemble a wide variety of proteins into structures with different symmetries.coiled coils | protein design | native mass spectrometry | analytical ultracentrifugation | cryoelectron microscopy

SignificanceTranscriptional coactivators and their partner transcription factors have been labeled as intrinsically disordered, fuzzy, and undruggable. We propose that the identification of conserved mechanisms of engagement between coactivators and their cognate activators should provide general principles for small-molecule modulator discovery. Here, we show that the structurally divergent coactivator Med25 forms short-lived and dynamic complexes with three different transcriptional activators and that conformational shifts are mediated by a flexible substructure of two dynamical helices and flanking loops. Analogous substructures are found across coactivators. Further, targeting one of the flexible structures with a small molecule modulates Med25–activator complexes. Thus, the two conclusions of the work are actionable for the discovery of small-molecule modulators of this functionally important protein class.

A key functional event in eukaryotic gene activation is the formation of dynamic protein–protein interaction networks between transcriptional activators and transcriptional coactivators. Seemingly incongruent with the tight regulation of transcription, many biochemical and biophysical studies suggest that activators use nonspecific hydrophobic and/or electrostatic interactions to bind to coactivators, with few if any specific contacts. Here a mechanistic dissection of a set of representative dynamic activator•coactivator complexes, comprised of the ETV/PEA3 family of activators and the coactivator Med25, reveals a different molecular recognition model. The data demonstrate that small sequence variations within an activator family significantly redistribute the conformational ensemble of the complex while not affecting overall affinity, and distal residues within the activator—not often considered as contributing to binding—play a key role in mediating conformational redistribution. The ETV/PEA3•Med25 ensembles are directed by specific contacts between the disordered activator and the Med25 interface, which is facilitated by structural shifts of the coactivator binding surface. Taken together, these data highlight the critical role coactivator plasticity plays in recognition of disordered activators and indicate that molecular recognition models of disordered proteins must consider the ability of the binding partners to mediate specificity.

The protein-protein interaction between menin and mixed-lineage leukemia 1 (MLL1) plays an important role in development of acute leukemia with translocations of the MLL1 gene and in solid tumors. Here, we report the development of a new generation of menin-MLL1 inhibitors identified by structure-based optimization of the thienopyrimidine class of compounds. This work resulted in compound 28 (MI-1481), which showed very potent inhibition of the menin-MLL1 interaction (IC = 3.6 nM), representing the most potent reversible menin-MLL1 inhibitor reported to date. The crystal structure of the menin-28 complex revealed a hydrogen bond with Glu366 and hydrophobic interactions, which contributed to strong inhibitory activity of 28. Compound 28 also demonstrates pronounced activity in MLL leukemia cells and in vivo in MLL leukemia models. Thus, 28 is a valuable menin-MLL1 inhibitor that can be used for potential therapeutic applications and in further studies regarding the role of menin in cancer.

Protein-protein interactions (PPI) between the transcriptional repressor B-cell lymphoma 6 (BCL6) BTB domain (BCL6) and its corepressors have emerged as a promising target for anticancer therapeutics. However, identification of potent, drug-like inhibitors of BCL6 has remained challenging. Using NMR-based screening of a library of fragment-like small molecules, we have identified a thiourea compound (7CC5) that binds to BCL6. From this hit, the application of computer-aided drug design (CADD), medicinal chemistry, NMR spectroscopy, and X-ray crystallography has yielded an inhibitor, 15f, that demonstrated over 100-fold improved potency for BCL6. This gain in potency was achieved by a unique binding mode that mimics the binding mode of the corepressor SMRT in the aromatic and the HDCH sites. The structure-activity relationship based on these new inhibitors will have a significant impact on the rational design of novel BCL6 inhibitors, facilitating the identification of therapeutics for the treatment of BCL6-dependent tumors.

GAS41 is a chromatin-associated protein that belongs to the YEATS family and is involved in the recognition of acetyl-lysine in histone proteins. A unique feature of GAS41 is the presence of a C-terminal coiled-coil domain, which is responsible for protein dimerization. Here, we characterized the specificity of the GAS41 YEATS domain and found that it preferentially binds to acetylated H3K18 and H3K27 peptides. Interestingly, we found that full-length, dimeric GAS41 binds to diacetylated H3 peptides with an enhanced affinity when compared to those for monoacetylated peptides, through a bivalent binding mode. We determined the crystal structure of the GAS41 YEATS domain with H3K23acK27ac to visualize the molecular basis of diacetylated histone binding. Our results suggest a unique binding mode in which full-length GAS41 is a reader of diacetylated histones.

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