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Leishmania braziliensis Protein Arginine Methyltransferases interactomes

ABSTRACT: We functionally characterized the five predicted PRMTs in Leishmania braziliensis by gene knockout and endogenous protein HA tagging using CRISPR/Cas9 gene editing. We report that R-methylation profiles vary among Leishmania species and across L. braziliensis lifecycle stages, with the peak PRMT expression occurring in promastigotes. A list of PRMT-interacting proteins was obtained in a single coimmunoprecipitation assay using HA-tagged PRMTs, suggesting a network of putative targets of PRMTs and cooperation between the R-methylation writers. Knockout of each L. braziliensis PRMT led to significant changes in global arginine methylation patterns without affecting cell viability. Deletion of either PRMT1 or PRMT3 disrupted most type I PRMT activity, resulting in a global increase in monomethyl arginine levels. Using anti-MMA antibodies, we performed an IP experiment to identify MMA proteins in the parental line, single PRMT1 knockout, PRMT1/PRMT7 double knockout and PRMT1-Addback parasites. The results indicate that R-methylation is modulated across lifecycle stages in L. braziliensis and show possible functional overlap and cooperation among the different PRMTs in targeting proteins. Overall, our data suggest important regulatory roles of these proteins throughout the L. braziliensis life cycle, showing that arginine methylation is important for parasite-host cell interactions. Linked publication: https://doi.org/10.1101/2021.09.22.461376.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Leishmania Braziliensis

DISEASE(S): Leishmaniasis

SUBMITTER: Lissur Orsine

LAB HEAD: Angela Kaysel Cruz

PROVIDER: PXD031057 | Pride | 2022-03-03

REPOSITORIES: Pride

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Project description:Arginine methylation is essential for both cellular viability and development and is also dysregulated in cancer. PRMTs catalyze the post translational monomethylation (Rme1/MMA, catalyzed by Type I-III), asymmetric (Rme2a/ADMA, Type I enzymes)-, or symmetric (Rme2s/SDMA, Type II enzymes) dimethylation of arginine. Despite many studies, a thorough integration of PRMT enzyme substrate determination and proteomic and transcriptomic consequences of inhibiting Type I and II PRMTs is lacking. To characterize cellular substrates for Type I (Rme2a) and Type II (Rme2s) PRMTs, human A549 lung adenocarcinoma cells were treated with either Type I (MS023) or Type II (GSK591) inhibitors. Using total proteome hydrolysis, we developed a new mass spectrometry approach to analyze total arginine and lysine content. We showed that Rme1 was a minor population (~0.1% of total arginine), Rme2a was highly abundant (~1.1%), and Rme2s was intermediate (~0.4%). While Rme2s was mostly eliminated by GSK591 treatment, total Rme1 and Rme2a were more resistant to perturbation. To quantitatively characterize substrate preferences of the major enzymes PRMT1, PRMT4(CARM1), and PRMT5, we used oriented peptide array libraries (OPAL) in methyltransferase assays. We demonstrated that while PRMT5 tolerates aspartic acid residues in the substrate, PRMT1 does not. Importantly, PRMT4 methylated previously uncharacterized hydrophobic motifs. To integrate our studies, we performed PTMScan on PRMT-inhibited A549 cells and enriched for methylated arginine containing tryptic peptides. For detection of highly charged peptides, a method to analyze the samples using electron transfer dissociation was developed. Proteomic analysis revealed distinct methylated species enriched in nuclear function, RNA-binding, intrinsically disordered domains, and liquid-liquid phase separation. Parallel studies with proteomics and RNA-Seq revealed distinct, but ontologically overlapping, consequences to PRMT inhibition. Overall, we demonstrate a wider PRMT substrate diversity and methylarginine functional consequence than previously shown.

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.

Project description:Protein arginine methylation, catalyzed by the protein arginine methyltransferase (PRMT) family, is recognized as a widespread post-translational modification (PTM) with implications in a plethora of biological processes in eukaryotes. PRMT proteins were classified into three types, type I, II and III, according to the final methyl-arginine products generated. Despite that thousands of substrates have been identified for Type I and II PRMTs, a full scope of arginine methylation catalyzed by the only type III PRMT, PRMT7, as well as its connection with that of type I and II PRMTs remain unknown, limiting our understanding of the network of arginine methylation and its functions in cells. In this study, global profiling of PRMT4 (type I), PRMT5 (type II) and PRMT7 (type III) substrates (also referred as methylome) revealed that PRMT7 methylated a GAR (glycine and arginine) motif similar as PRMT5, while PRMT4 uniquely methylated a motif in which proline was highly enriched. PRMT4, 5 and 7-methylome were all enriched with proteins functioning in mRNA splicing, and knockdown of PRMT4, 5 or 7 led to a global change of alternative splicing events, among which a cohort with implications in cancer development was co-regulated by all three PRMTs. PRMT4, 5 and 7-mediated arginine methylation on splicing factors such as hnRNPA1, though at different status, were shown to enhance RNA binding in general and participate in the regulation of PRMT4, 5 and 7 co-regulated alternative splicing events.The clinical significance of PRMT4, 5 and 7-mediated arginine methylation was underscored by the fact that these three PRMTs as well as hnRNPA1 arginine methylation were over-represented in multiple types of cancers, which were associated with aberrant gene alternative splicing. Consistently, silencing or pharmacological inhibition of PRMT4, 5 and 7 altered gene alternative splicing and suppressed cancer cell growth, and co-treatment exhibited synergistic effects. Taken together, our study provided an integrative view of substrates for the three types of PRMTs, revealing the important function of arginine methylation in RNA splicing and cancer.

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Leishmania braziliensis Protein Arginine Methyltransferases interactomes

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