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Profiling nuclear cysteine ligandability and effects on nuclear localization using proximity labeling-coupled chemoproteomics

ABSTRACT: The nucleus controls cell growth and reproduction by well-orchestrated interactions between nuclear proteins and chromatin. Mutations that result in the dysregulation of these chromatin-associated proteins are known to lead to the onset of numerous diseases. Many of these nuclear proteins have remained recalcitrant to traditional non-covalent small-molecule ligand discovery. Covalent ligands can provide a promising approach for targeting proteins such as transcription factors that lack ordered small-molecule binding pockets. Here, we present a chemoproteomic platform that couples proximity labeling (PL) using a Histone-TurboID (His-TID) construct with competitive isoTOP-ABPP to identify ligandable nuclear cysteines. Application of covalent scout fragments, KB02 and KB05, revealed ligandable cysteine sites on diverse proteins involved in transcriptional regulation, spindle assembly, and DNA repair. To identify functional liganding events that alter target-protein association with chromatin, we monitor the effects of KB02 and KB05 on the chromatin-associated proteome. Importantly, we identify proteins that show both increased and decreased association with chromatin in the presence of the covalent fragments. Notably, the Parkinson disease protein 7 (PARK7) showed increased nuclear localization and association with chromatin upon covalent liganding at Cys106 by KB02. Together, our PL-assisted nuclear-focused chemoproteomic platform provides us insights into nuclear cysteine ligandability and the functional effects of ligand binding on chromatin association, thereby furthering our understanding of the potentially druggability of the nuclear proteome.

INSTRUMENT(S): Orbitrap Exploris 240

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture, Hela Cell

SUBMITTER: Qianni Peng

LAB HEAD: Eranthie Weerapana

PROVIDER: PXD043732 | Pride | 2024-01-24

REPOSITORIES: Pride

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Project description:Numerous reagents have been developed to enable chemical proteomic analysis of small molecule-protein interactomes. However, the performance of these reagents has not been systematically evaluated and compared. Herein, we report our efforts to conduct a parallel assessment of two widely-used chemically-cleavable linkers equipped with dialkoxydiphenylsilane (DADPS linker) and azobenzene (AZO linker) moieties. Profiling a cellular cysteinome using iodoacetamide alkyne probe demonstrated a significant discrepancy between the experimental results obtained through the application of each of the reagents. To better understand the source of observed discrepancy, a mass tolerant database search strategy using MSFragger software was performed. This resulted in identifying a previously unreported artifactual modification on the residual mass of the azobenzene linker. Furthermore, we conducted a comparative analysis of enrichment modes using both cleavable linkers. This effort determined that enrichment of proteolytic digests yielded a far greater number of identified cysteine residues than the enrichment conducted prior to protein digest. Inspired by recent studies where multiplexed quantitative labeling strategies were applied to cleavable biotin linkers, we combined this further optimized protocol using the DADPS cleavable linker with tandem mass tag (TMT) labeling to profile the FDA-approved covalent EGFR kinase inhibitor dacomitinib against the cysteinome of an epidermoid cancer cell line. Our analysis resulted in the detection and quantification of over 10,000 unique cysteine residues, a nearly 3-fold increase over previous studies that used cleavable biotin linkers for enrichment. Critically, cysteine residues corresponding to proteins directly as well as indirectly modulated by dacomitinib treatment were identified. Overall, our study suggests that the dialkoxydiphenylsilane linker could be broadly applied wherever chemically cleavable linkers are required for chemical proteomic characterization of cellular proteomes.

Dataset Information

Profiling nuclear cysteine ligandability and effects on nuclear localization using proximity labeling-coupled chemoproteomics

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