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Antibodies against the mono-methylated Arginine-Glycine repeat (MMA-RG) of the Epstein-Barr virus nuclear antigen 1 (EBNA1) identify potential cellular proteins targeted in viral transformation

ABSTRACT: The viral nuclear antigen 1 (EBNA1) of Epstein Barr (EBV) features two functionally redundant Arginine-Glycine (RG) repeats that contain symmetrically and asymmetrically di-methylated (SDMA/ADMA) and also mono-methylated (MMA) Arginine residues. We generated mouse monoclonal antibodies against the mono-methylated RG-repeat between aa 328-377. In addition to detect MMA-EBNA1, we aimed at the identification of cellular proteins that are bound to MMA-modified EBNA1 in EBV-positive Raji cells.

INSTRUMENT(S): Q Exactive HF-X

ORGANISM(S): Homo Sapiens (human) Human Herpesvirus 4

TISSUE(S): Raji Cell

SUBMITTER: Thomas Fröhlich

LAB HEAD: Thomas Fröhlich

PROVIDER: PXD051181 | Pride | 2025-03-05

REPOSITORIES: pride

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Use of antibodies against Epstein-Barr virus nuclear antigen 1 for detection of cellular proteins with monomethylated arginine residues that are potentially involved in viral transformation.

Graesser Christian C Nord Ruth R Flaswinkel Heinrich H Kremmer Elisabeth E Meese Eckart E Caban Karolina Magdalena KM Fröhlich Thomas T Grässer Friedrich A FA Hart Martin M

Archives of virology 20241108 12

Epstein-Barr virus nuclear antigen 1 (EBNA1) contains two arginine-glycine (RG) repeats that contain symmetric/asymmetric dimethylarginine (SDMA/ADMA) and monomethylarginine (MMA) residues. We generated mouse monoclonal antibodies directed against a monomethylated GRGRGG-containing repeat located between amino acids 328 and 377 of EBNA1. In addition to detecting MMA-modified EBNA1, we also had the goal of identifying cellular proteins that bind to MMA-modified EBNA1 in EBV-positive Raji cells. F ...[more]

PMID: 39514105

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Project description:The covalent attachment of methyl groups to the side-chain of arginine residues is known to play essential roles in regulation of transcription, protein function and RNA metabolism. The specific N-methylation of arginine residues is catalyzed by a small family of gene products known as protein arginine methyltransferases; however, very little is known about which arginine residues become methylated on target substrates. Here we describe an unbiased methodology that combines single-step immunoenrichment of methylated peptides with high-resolution mass spectrometry to identify endogenous arginine mono-methylation (MMA) sites. We thereby identify 1,027 site-specific MMA sites on 494 human proteins, discovering numerous novel mono-methylation targets and confirming the majority of currently known MMA substrates. Nuclear RNA-binding proteins involved in RNA processing, RNA localization, transcription, and chromatin remodeling are prominently found modified with MMA. Despite this, MMA sites prominently are located outside RNA-binding domains as compared to the proteome-wide distribution of arginine residues. Quantification of arginine methylation in cells treated with Actinomycin D uncovers strong site-specific regulation of MMA sites during transcriptional arrest. Interestingly, several MMA sites are down-regulated after a few hours of under transcriptional arrest. In contrast, the corresponding di-methylation or protein expression level is not altered in expression, confirming that MMA sites contain regulated functions on their own. Collectively, we present a site-specific MMA dataset in human cells and demonstrate for the first time that MMA is a dynamic post-translational modification regulated during transcriptional arrest by a hitherto uncharacterized arginine demethylase. Data analysis: All raw data analysis was performed with MaxQuant software suite version 1.2.6.20 supported by the Andromeda search engine. Data was searched against a concatenated target/decoy (forward and reversed) version of the UniProtKB Human database encompassing 71,434 protein entries. Mass tolerance for searches was set to maximum 7 ppm for peptide masses and 20 ppm for HCD fragment ion masses. Data was searched with carbamidomethylation as a fixed modification and protein N-terminal acetylation, methionine oxidation and mono-methylation on lysine and arginine as variable modifications. A maximum of three mis-cleavages was allowed while requiring strict trypsin specificity, and only peptides with a minimum sequence length of seven were considered for further data analysis. Peptide assignments were statistically evaluated in a Bayesian model on the basis of sequence length and Andromeda score. Only peptides and proteins with a false discovery rate (FDR) of less than 1% were accepted, estimated on the basis of the number of accepted reverse hits. Protein sequences of common contaminants such as human keratins and proteases used were added to the database.

Project description:Protein methylation has been implicated in many important biological contexts including signaling, metabolism, and transcriptional control. Despite the importance of this post- translational modification, the global analysis of protein methylation by mass spectrometry-based proteomics has not been extensively studied due to the lack of robust, well-characterized techniques for methyl-peptidemethyl peptide enrichment. Here, to better investigate protein methylation, we optimized and compared two methods for methyl-peptidemethyl peptide enrichment: immunoaffinity purification (IAP) and high pH strong cation exchange (SCX). Comparison of these methods revealed that they are largely orthogonal for monomethyl arginine (MMA), suggesting that the usage of both techniques is required to provide a global view of protein methylation. Using both IAP and SCX, we investigated changes in protein methylation downstream of protein arginine methyltransferase 1 (PRMT1). Together, these techniques allowed us to quantify over ~1,000 arginine methylation sites on 407 proteins. Of these methylation sites, PRMT1 knockdown resulted in significant changes to 110 arginine methylation sites on 59 proteins. In contrast, zero lysine methylation sites were significantly changed upon PRMT1 knockdown. In PRMT1 knockdown cells, 24 MMA sites exhibited both significant downregulation (ie, putative PRMT1-mediated MMA targets) and 63 significant upregulation (ie, putative PRMT1-mediated ADMA targets). PRMT1 knockdown induced significant changes in asymmetric dimethyl arginine (ADMA), consistent with being PRMT1 targets. Additionally, We also observed that PRMT1 knockdown induced significant increases in symmetric dimethyl arginine (SDMA) methylation, suggesting that loss of PRMT1 activity allows scavenging of PRMT1 substrates by Type II PRMTs. Analysis of the subcellular localization and protein function of the significantly changing methyl-proteins revealed that the majority of PRMT1 substrates are localized to the nucleus and involved in RNA and DNA binding. Taken together, our results suggest that deep protein methylation profiling by mass spectrometry requires orthogonal enrichment techniques, identify novel PRMT1 methylation targets, and highlight in order to understand the dynamic interplay between methyltransferases in mammalian cells.

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