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Enhanced Proteomic Mapping of Arginine Methylation Using Electron Transfer Dissociation Reveals Novel PRMT5 Substrates and Arginine Trimethylation

ABSTRACT: PRMT5 is the major enzyme that catalyzes the symmetric dimethylation of arginine (sDMA) in mammalian cells. Its activity is crucial for many biological processes including transcriptional regulation, mRNA processing, as well as DNA damage and repair. However, the protein substrates identified for PRMT5 have yet been limited in numbers, hindering the understanding of PRMT5 functions in normal as well as diseased cells. Herein we developed an optimized strategy for proteomic profiling of cellular sDMA and apply it to the discovery of novel PRMT5 substrates. Our results show that a combination of proteolytic digestion by the metalloprotease ulilysin and using electron-transfer dissociation with supplemental activation as the mass spectrometry method significantly increased sDMA site identification and localization after immuno-affinity enrichment. By employing SILAC-based differential quantitative proteomic approach and a PRMT5 specific inhibitor, we identified 325 sDMA sites being regulated by PRMT5, 220 being novel sites, which greatly expanded the number of PRMT5 substrates. Biochemical studies confirmed the newly discovered PRMT5 substrate, Plasminogen activator inhibitor 1 RNA-binding protein (SERBP1) and revealed that the RGG/RG motif in the central region of SERBP1 contains both PRMT5-catalyzed sDMA and Type I PRMT-catalyzed asymmetric dimethylation of arginine (aDMA). Unexpectedly, using the optimized methylarginine profiling strategy, we also discovered arginine trimethylation, a previously unknown type of modification, on the central RGG/RG region of SERBP1. By mutational studies we demonstrated that the trimethyl modification on R172 of SERBP1 regulates its recruitment to stress granule (SG) under oxidative stress, indicating a functional role of arginine trimethylation in the cell. Overall, the optimized profiling strategy not only enabled the identification of extensive, non-overlapping sDMA sites and novel PRMT5 substrates, but also revealed a potentially important new PTM, arginine trimethylation. The work lays the foundation for further investigations on the functional interplay of different methylation modifications on arginines, especially in the heavily methylated RGG/RG motif of many RNA-binding proteins.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Zilu Ye

LAB HEAD: Jesper Olsen

PROVIDER: PXD037425 | Pride | 2024-04-30

REPOSITORIES: Pride

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			Action	DRS
	20181130_ULILYSIN_PTMscan_LLZ_2h_10HCD_1ul_slowgradient.raw	Raw
	20181130_ULILYSIN_PTMscan_LLZ_2h_10HCD_1ul_slowgradient.xlsx	Xlsx
	20190115_Hela_trypsin_stagetip_LLZ_2h_10HCD_2ul_slowgradient-_1_.xlsx	Xlsx
	20190115_Hela_trypsin_stagetip_LLZ_2h_10HCD_2ul_slowgradient.raw	Raw
	20210105_LUMOS1_nLC6_ZY_SA_Hela_Ulilysin_IAP_ETD0-_1_.pdResult	Other

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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.

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Enhanced Proteomic Mapping of Arginine Methylation Using Electron Transfer Dissociation Reveals Novel PRMT5 Substrates and Arginine Trimethylation

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