Project description:Targeting cellular RNA by small molecules has come to the forefront of biotechnology and holds great promise for therapeutic use. Strategies to identify, validate and optimize these molecules are essential, but are still lacking in some aspects. In particular, the site-specific covalent labeling and modification of RNA in living cells poses many challenges. Here, we describe a general structure-guided approach to engineer non-covalent RNA aptamer–ligand complexes into their covalent counterparts using a molecular tether. The key is to modify the native ligand with an electrophilic handle that allows it to react specifically with a guanine at the RNA ligand binding site. We show that site-specific cross-linking between ligand and RNA is achieved in mammalian cells upon transfection of a genetically encoded version of the preQ1-I riboswitch aptamer. Further, we showcase the versatility of the tether by engineering the first covalent fluorescent light-up aptamer (coFLAP) out of the non-covalent Pepper FLAP. The coPepper system maintains strong fluorescence in live-cell imaging even after repeated washing. Thus, any background signal arising from unspecific fluorophore accumulation in the cell can be eliminated. In addition, we generated a bifunctional Pepper ligand containing a second handle for bioorthogonal chemistry to allow for easily traceable and efficient pulldown of the covalently linked target RNA. Finally, we provide evidence for the suitability of this tethering strategy for specific drug targeting. Taken together, our results show that functionalized ligands generated by rational design can cross-link site-specifically with target RNAs in cells, and hence, open up a wide range of applications in RNA biology that require irreversible small molecule binding.
Project description:A Phase 1/1b dose finding study to determine the OBD(s) and RP2D(s) of BMF-219, a covalent menin inhibitor small molecule, in subjects with KRAS mutated unresectable, locally advanced, or metastatic NSCLC (Cohort 1), PDAC (Cohort 2), and CRC (Cohort 3).
Project description:Chromosome organization by structural maintenance of chromosomes (SMC) complexes is vital to living organisms. SMC complexes were recently found to be motors that extrude DNA loops. However, it remains unclear what happens when multiple complexes encounter one another in vivo on the same DNA and how interactions help organize an active genome. We created a crash-course track system to study SMC complex encounters in vivo by engineering the Bacillus subtilis chromosome to have defined SMC loading sites. Chromosome conformation capture (Hi-C) analyses of over 20 engineered strains show an amazing variety of never-before-seen chromosome folding patterns. Via 3D polymer simulations and theory, we find that these patterns require SMC complexes to bypass each other in vivo, as recently seen in an in vitro study. We posit that the bypassing activity enables SMC complexes to spatially organize a functional and busy genome.
Project description:Visualizing and measuring molecular-scale interactions in living cells represents a major challenge, but recent advances in microscopy are bringing us closer to achieving this goal. Single-molecule super-resolution microscopy enables high-resolution and sensitive imaging of the positions and movement of molecules in living cells. HP1 proteins are important regulators of gene expression because they selectively bind and recognize H3K9 methylated (H3K9me) histones to form heterochromatin-associated protein complexes that silence gene expression. Here, we extended live-cell single-molecule tracking studies in fission yeast to determine how HP1 proteins interact with their binding partners in the nucleus. We measured how genetic perturbations that affect H3K9me alter the diffusive properties of HP1 proteins and each of their binding partners based on which we inferred their most likely interaction sites. Our results indicate that H3K9me promotes specific complex formation between HP1 proteins and their interactors in a spatially restricted manner, while attenuating their ability to form off-chromatin complexes. As opposed to being an inert platform or scaffold to direct HP1 binding, our studies propose a novel function for H3K9me as an active participant in enhancing HP1-associated complex formation in living cells.
Project description:Effective and convenient covalent protein conjugation could benefit diverse biological systems, stabilizing key protein protein interactions which are otherwise reversible. Neisseria meningitidis contains a protein which undergoes autoproteolysis via an anhydride. Here, we harness this spontaneously generated electrophile for covalent targeting of unmodified endogenous proteins. In ‘NeissLock’, a binding protein genetically fused to the self-processing module (SPM) docks to its target protein. Upon triggering with calcium, the aspartic anhydride generated at the C-terminus of the binding protein allows nucleophilic attack by nearby residues on the target protein, so ligating the proteins. We established a computational tool to search the Protein Data Bank, assessing proximity of amines to C-termini. We validated and optimized the NeissLock concept using the Ornithine Decarboxylase/Antizyme complex. A range of nucleophiles on the target (α-amine or ε-amines) could rapidly react with the anhydride, but reaction was blocked if the partner protein did not dock. Surprisingly, the optimal pH for covalent ligation was 7.0. We then armed Transforming Growth Factor-α with SPM and established covalent targeting to Epidermal Growth Factor Receptor at the surface of living cells. NeissLock harnesses exceptional protein chemistry to allow covalent targeting of endogenous proteins under mild conditions with up to 80% yield, allowing new possibilities for molecular engineering.
Project description:Understanding which proteins are presented at the cell surface is essential for ongoing therapeutic development, and to expand our basic understanding of biology. We envisioned the integration of cell surface engineering with radical-mediated protein biotinylation to profile cell surface proteins (CSPs). This method relies on the pre-functionalization of cells with cholesterol lipid groups, followed by their conjugation with an APEX2 ascorbate peroxidase enzyme. The APEX2 enzyme allows for the covalent conjugation of biotin moieties to nearby residues for subsequent enrichment, and serves as a tool for the enrichment and subsequent MS analysis of CSPs.
Project description:Understanding how small molecules bind to specific protein complexes in living cells is critical to understanding their mechanism-of-action. Unbiased chemical biology strategies for direct readout of protein interactome remodelling by small molecules would provide advantages over target-focused approaches, including the ability to detect previously unknown ligand targets and complexes. However, there are few current methods for unbiased profiling of small molecule interactomes. To address this, we envisioned a technology that would combine the sensitivity and live-cell compatibility of proximity labelling coupled to mass spectrometry, with the specificity and unbiased nature of photoaffinity labelling. In this manuscript, we describe the BioTAC system, a small-molecule guided proximity labelling platform that can rapidly identify both direct and complexed small molecule binding proteins. We benchmark the system against µMap, photoaffinity labelling, affinity purification coupled to mass spectrometry and proximity labelling coupled to mass spectrometry datasets. We also apply the BioTAC system to provide interactome maps of Trametinib and analogues. The BioTAC system overcomes a limitation of current approaches and supports identification of both inhibitor bound and molecular glue bound complexes.