Thursday, November 25, 2021

Site-Specific Labeling of Endogenous Proteins Using CoLDR Chemistry

Rambabu N. Reddi, Adi Rogel, Efrat Resnick, Ronen Gabizon, Pragati Kishore Prasad, Neta Gurwicz, Haim Barr, Ziv Shulman, and Nir London

Journal of the American Chemical Society 2021

DOI: 10.1021/jacs.1c06167

Chemical modifications of native proteins can affect their stability, activity, interactions, localization, and more. However, there are few nongenetic methods for the installation of chemical modifications at a specific protein site in cells. Here we report a covalent ligand directed release (CoLDR) site-specific labeling strategy, which enables the installation of a variety of functional tags on a target protein while releasing the directing ligand. Using this approach, we were able to label various proteins such as BTK, K-RasG12C, and SARS-CoV-2 PLpro with different tags. For BTK we have shown selective labeling in cells of both alkyne and fluorophores tags. Protein labeling by traditional affinity methods often inhibits protein activity since the directing ligand permanently occupies the target binding pocket. We have shown that using CoLDR chemistry, modification of BTK by these probes in cells preserves its activity. We demonstrated several applications for this approach including determining the half-life of BTK in its native environment with minimal perturbation, as well as quantification of BTK degradation by a noncovalent proteolysis targeting chimera (PROTAC) by in-gel fluorescence. Using an environment-sensitive “turn-on” fluorescent probe, we were able to monitor ligand binding to the active site of BTK. Finally, we have demonstrated efficient CoLDR-based BTK PROTACs (DC50 < 100 nM), which installed a CRBN binder onto BTK. This approach joins very few available labeling strategies that maintain the target protein activity and thus makes an important addition to the toolbox of chemical biology.

Wednesday, November 24, 2021

Chemoproteomic Profiling by Cysteine Fluoroalkylation Reveals Myrocin G as an Inhibitor of the Nonhomologous End Joining DNA Repair Pathway [@AdibekianG]

Daniel Abegg, Martin Tomanik, Nan Qiu, Dany Pechalrieu, Anton Shuster, Bruno Commare, Antonio Togni, Seth B. Herzon, and Alexander Adibekian

Journal of the American Chemical Society 2021

DOI: 10.1021/jacs.1c09724

Chemoproteomic profiling of cysteines has emerged as a powerful method for screening the proteome-wide targets of cysteine-reactive fragments, drugs, and natural products. Herein, we report the development and an in-depth evaluation of a tetrafluoroalkyl benziodoxole (TFBX) as a cysteine-selective chemoproteomic probe. We show that this probe features numerous key improvements compared to the traditionally used cysteine-reactive probes, including a superior target occupancy, faster labeling kinetics, and broader proteomic coverage, thus enabling profiling of cysteines directly in live cells. In addition, the fluorine “signature” of probe 7 constitutes an additional advantage resulting in a more confident adduct–amino acid site assignment in mass-spectrometry-based identification workflows. We demonstrate the utility of our new probe for proteome-wide target profiling by identifying the cellular targets of (−)-myrocin G, an antiproliferative fungal natural product with a to-date unknown mechanism of action. We show that this natural product and a simplified analogue target the X-ray repair cross-complementing protein 5 (XRCC5), an ATP-dependent DNA helicase that primes DNA repair machinery for nonhomologous end joining (NHEJ) upon DNA double-strand breaks, making them the first reported inhibitors of this biomedically highly important protein. We further demonstrate that myrocins disrupt the interaction of XRCC5 with DNA leading to sensitization of cancer cells to the chemotherapeutic agent etoposide as well as UV-light-induced DNA damage. Altogether, our next-generation cysteine-reactive probe enables broader and deeper profiling of the cysteinome, rendering it a highly attractive tool for elucidation of targets of electrophilic small molecules.

Improved Electrophile Design for Exquisite Covalent Molecule Selectivity [@BalynZaro]

José L. Montaño, Brian J. Wang, Regan F. Volk, Virginia G. Garda, Balyn W. Zaro*

ChemRxiv, 2021

D O I: 10.26434/chemrxiv-2021-67z8j-v2 [opens in a new tab]

Covalent inhibitors continue to show therapeutic promise. However, off-target reactivity challenges the field. Extensive efforts have been exerted to solve this issue by varying the reactivity attributes of electrophilic warheads, with features such as reversibility or metabolic vulnerability. Here we report the development of a new approach to increase the selectivity of covalent probes and small molecule inhibitors that is independent of warhead reactivity features and can be used in concert with already-existing methods. Using the Bruton’s Tyrosine Kinase (BTK) inhibitor Ibrutinib scaffold for our proof-of-concept, we reasoned that increasing the steric bulk of fumarate-based electrophiles on Ibrutinib should improve selectivity via the steric exclusion of off-targets but ideally retain rates of cysteine reactivity comparable to that of an acrylamide. Using chemical proteomic techniques, we demonstrate that elaboration of the electrophile to a tert-Butyl (t-Bu) fumarate ester significantly decreases time-dependent off-target reactivity and abolishes time-independent off-target reactivity but retains BTK target engagement. While an alkyne-bearing probe analog of Ibrutinib has 247 protein targets, our t-Bu fumarate Ibrutinib probe analog has only 7 protein targets. Of these 7 targets, BTK is the only time-independent target. This 2-order-of-magnitude increase in selectivity is also conferred to the t-Bu inhibitor itself. By shotgun proteomics, we investigated the consequences of treatment with Ibrutinib and our t-Bu analog and discovered that only 8 proteins are downregulated in response to treatment with the t-Bu analog compared to 107 with Ibrutinib. Of these 8 proteins, 7 are also downregulated by Ibrutinib and a majority of these targets are associated with BTK biology. Taken together, these findings reveal a previously-unappreciated opportunity to increase cysteine-reactive covalent inhibitor selectivity through electrophilic structure optimization.

Friday, November 19, 2021

Metabolically Activated Proteostasis Regulators Protect against Glutamate Toxicity by Activating NRF2

Jessica D. Rosarda, Kelsey R. Baron, Kayla Nutsch, Gabriel M. Kline, Caroline Stanton, Jeffery W. Kelly, Michael J. Bollong, and R. Luke Wiseman

ACS Chemical Biology 2021

DOI: 10.1021/acschembio.1c00810

The extracellular accumulation of glutamate is a pathologic hallmark of numerous neurodegenerative diseases including ischemic stroke and Alzheimer’s disease. At high extracellular concentrations, glutamate causes neuronal damage by promoting oxidative stress, which can lead to cellular death. This has led to significant interest in developing pharmacologic approaches to mitigate the oxidative toxicity caused by high levels of glutamate. Here, we show that the small molecule proteostasis regulator AA147 protects against glutamate-induced cell death in a neuronal-derived cell culture model. While originally developed as an activator of the activating transcription factor 6 (ATF6) arm of the unfolded protein response, this AA147-dependent protection against glutamate toxicity is primarily mediated through activation of the NRF2-regulated oxidative stress response. We demonstrate that AA147 activates NRF2 selectively in neuronal-derived cells through a mechanism involving metabolic activation to a reactive electrophile and covalent modification of KEAP1─a mechanism analogous to that involved in the AA147-dependent activation of ATF6. These results define the potential for AA147 to protect against glutamate-induced oxidative toxicity and highlight the potential for metabolically activated proteostasis regulators like AA147 to activate both protective ATF6 and NRF2 stress-responsive signaling pathways to mitigate oxidative damage associated with diverse neurologic diseases.

Monday, November 15, 2021

Tunable Amine-Reactive Electrophiles for Selective Profiling of Lysine [@Keribackus, @MonikaRaj_lab ]

Monika Raj, Kuei-Chien Tang,Jian Cao, Lisa M. Boatner, Linwei Li,Jonathan Farhi, Kendall N. Houk, Jennifer Spangle, Keriann M. Backus

Angewandte Chemie, 2021

Proteome profiling by activated esters identified >9000 ligandable lysines but they are limited as covalent inhibitors due to poor hydrolytic stability. Here we report our efforts to design and discover a new series of Tunable Amine- Reactive  lEectrophiles (TAREs) for selective and robust labeling of lysine. The major challenges in developing selective covalent ligands for lysine are the high nucleophilicity of cysteines and poor hydrolytic stability. Our work circumvents these challenges by a unique design of the TAREs that form stable adducts with lysine and on reaction with cysteine generate another reactive electrophiles for lysine. We highlight that TAREs exhibit substantially high hydrolytic stability as compared to the activated esters and are non-cytotoxic thus have the potential to act as covalent ligands. We applied these alternative TAREs for the intracellular labeling of proteins, and for the selective identification of lysines in the human proteome on a global scale.

Sunday, November 14, 2021

Proximity-Dependent Labeling of Cysteines [@Pthompsn1018, @jusudeshna]

Sudeshna Sen, Nadia Sultana, Scott A. Shaffer, and Paul R. Thompson
Journal of the American Chemical Society 2021

DOI: 10.1021/jacs.1c07069

Mapping protein–protein interactions is crucial for understanding various signaling pathways in living cells, and developing new techniques for this purpose has attracted significant interest. Classic methods (e.g., the yeast two-hybrid) have been supplanted by more sophisticated chemical approaches that label proximal proteins (e.g., BioID, APEX). Herein we describe a proximity-based approach that uniquely labels cysteines. Our approach exploits the nicotinamide N-methyltransferase (NNMT)-catalyzed methylation of an alkyne-substituted 4-chloropyridine (SS6). Upon methylation of the pyridinium nitrogen, this latent electrophile diffuses out of the active site and labels proximal proteins on short time scales (≤5 min). We validated this approach by identifying known (and novel) interacting partners of protein arginine deiminase 2 (PAD2) and pyruvate dehydrogenase kinase 1 (PDK1). To our knowledge, this technology uniquely exploits a suicide substrate to label proximal cysteines in live cells.

Thursday, November 11, 2021

Mechanism-Based and Computational-Driven Covalent Drug Design [@lyna_yunluo]

Yun Lyna Luo

Journal of Chemical Information and Modeling 2021
DOI: 10.1021/acs.jcim.1c01278

Covalent drugs offer higher efficacy and longer duration of action than their noncovalent counterparts. Significant advances in computational methods for modeling covalent drugs are poised to shift the paradigm of small molecule therapeutics within the next decade. This viewpoint discusses the advantages of a two-state model for ranking reversible and irreversible covalent ligands and of more complex models for dissecting reaction mechanisms. The relation between these models highlights the complexity and diversity of covalent drug binding and provides opportunities for mechanism-based rational design.

Friday, November 5, 2021

Crystal structure of SARS-CoV-2 main protease in complex with protease inhibitor PF-07321332

Yao Zhao, Chao Fang, Qi Zhang, Ruxue Zhang, Xiangbo Zhao, Yinkai Duan, Haofeng Wang, Yan Zhu, Lu Feng, Jinyi Zhao, Maolin Shao, Xiuna Yang, Leike Zhang, Chao Peng, Kailin Yang, Dawei Ma, Zihe Rao & Haitao Yang 

Protein Cell, 2021

Thursday, November 4, 2021

Covalent Sortase A Inhibitor ML346 Prevents Staphylococcus aureus Infection of Galleria mellonella


Xiang-Na Guan,   Tao Zhang,   Teng Yang,   Ze Dong,   Song Yang, Jianhua Gan,   Le-Fu Lan  and  Cai-Guang Yang

The housekeeping sortase A (SrtA), a membrane-associated cysteine transpeptidase, is responsible for anchoring surface proteins to the cell wall peptidoglycan in Gram-positive bacteria. This process is essential for the regulation of bacterial virulence and pathogenicity. Therefore, SrtA is considered to be an ideal target for antivirulence therapy. In this study, we report that ML346, a compound with a barbituric acid and cinnamaldehyde scaffold, functions as an irreversible inhibitor of Staphylococcus aureus SrtA (SaSrtA) and Streptococcus pyogenes SrtA (SpSrtA) in vitro at low micromolar concentrations. According to our X-ray crystal structure of the SpSrtAΔN81/ML346 complex (Protein Data Bank ID: 7V6K), ML346 covalently modifies the thiol group of Cys208 in the active site of SpSrtA. Importantly, ML346 significantly attenuated the virulence phenotypes of S. aureus and exhibited inhibitory effects on Galleria mellonella larva infection caused by S. aureus. Collectively, our results indicate that ML346 has potential for development as a covalent antivirulence agent for treating S. aureus infections, including methicillin-resistant S. aureus. 

Thiol Reactivity of N-Aryl α-Methylene-γ-lactams: Influence of the Guaianolide Structure [@KayBrummond]

 Daniel P. Dempe, Chong-Lei Ji, Peng Liu, and Kay M. Brummond The Journal of Organic Chemistry, 2020 DOI: 10.1021/acs.joc.2c01530 The α-meth...