Chemical Labeling Research Articles

Abstract B032: Genome-wide 5-hydroxymethylation mapping in cell-free DNA to characterize the epigenetic differences in minimal residual disease of multiple myeloma

Abstract Background: Multiple myeloma (MM), a B-cell neoplasm characterized by the infiltration of malignant plasma cells into the bone marrow, is the second most common blood malignancy in the United States. The molecular pathogenesis of MM involves both genetic and epigenetic alterations. While 60-75% of newly diagnosed patients achieve a complete response or better with current modern combination therapies, almost all patients eventually progress largely due to the persistence or re-emergence of minimal residual disease (MRD). Monitoring for MRD has become essential for evaluating treatment efficacy and predicting long-term outcomes in MM patients. We aimed to investigate whether epigenetic changes, particularly 5- hydroxymethylcytosines (5hmC), at diagnosis are associated with MRD status following treatment. Methods: Utilizing 5hmC-Seal, a highly sensitive chemical labeling technique, we profiled genome-wide 5hmC in circulating cell-free DNA (cfDNA) and bone marrow genomic DNA (gDNA) at baseline and after 8 cycles of treatment (C8) from newly diagnosed MM patients (n=25) enrolled in a clinical trial (NCT01816971). MRD testing was performed on bone marrow samples using the clonoSEQ next generation sequencing assay (limit of detection 10-6). Results: The 5hmC modification levels were summarized across various genomic features, revealing enrichment in gene bodies and enhancer regions, consistent with the known regulatory role of 5hmC. We ranked 5hmC-modified genes at baseline by their variability, and found that the number of overlapping genes between cfDNA and gDNA was significantly higher than expected by permutation analysis. Subsequently, we identified the top 100 most variable 5hmC- modified genes in gDNA, which exhibited a higher Pearson correlation with cfDNA within individuals (mean r=0.90) compared to between individuals (mean r=0.82; p<0.05), suggesting that cfDNA has the potential to reflect gDNA in capturing some MM-related variations. Among the 11 patients with MRD+ at C8, a genome-wide scan of 5hmC in cfDNA comparing baseline and C8 identified 1,614 differentially modified genes (p<0.05) after adjusting for age and sex. [BC1] Furthermore, we identified 459 differentially modified genes comparing baseline 5hmC levels between patients who were MRD+ (n=11) and MRD- (n= 14) at C8 (p<0.05), after adjusting for age and sex. These results highlight the differential epigenetic landscape associated with MRD status. Conclusions: Genome-wide 5hmC profiling of cfDNA from blood revealed a similar epigenetic landscape to gDNA from bone marrow in patients with MM, suggesting that cfDNA may offer a less invasive alternative for assessing epigenetic modifications. Moreover, this profiling identified distinct epigenetic changes associated with the achievement of MRD- negativity. These findings provide a foundation for further investigation into the molecular alterations linked to MM disease biology that could potentially lead to MRD negativity. Future directions will focus on identifying biomarkers that could inform personalized treatment strategies. Citation Format: Zhou Zhang, Bei Wang, Krissana Kowitwanich, John Cursio, Daniel Appelbaum, Chuan He, Wei Zhang, Benjamin Derman, Brian Chiu, Andrzej Jakubowiak. Genome-wide 5-hydroxymethylation mapping in cell-free DNA to characterize the epigenetic differences in minimal residual disease of multiple myeloma [abstract]. In: Proceedings of the AACR Special Conference: Liquid Biopsy: From Discovery to Clinical Implementation; 2024 Nov 13-16; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(21_Suppl):Abstract nr B032.

Quantitative detection of pseudouridine in RNA by mass spectrometry.

Pseudouridine (Ψ) is one of the most prevalent and dynamic modification in RNA, and was shown to evade the host immune response in mRNA vaccines. Despite its significance, the biological role of Ψ remains poorly understood as certain key limitations and challenges in the detection of Ψ are yet to be overcome. In account of this, we report the usage of a chemical labelling strategy for the first quantitative detection of Ψ by mass spectrometry. We demonstrate a labelling efficiency exceeding 99% in isolated yeast tRNAs hosting multiple Ψs. LC-MS/MS analysis enables precise mapping of Ψ at single-base resolution, while simultaneously capturing a wide array of additional post-transcriptional modifications, which is not achieved with current sequencing technologies. This advancement may help unravel the dynamics and biological implications of Ψ, shedding light on its interplay with other modifications and deepening our understanding of its functional role.

Rapid Detection of Single Bacteria Using Filter-Array-Based Hyperspectral Imaging Technology.

Rapid and accurate detection of bacterial pathogens is crucial for preventing widespread public health crises, particularly in the food industry. Traditional methods are often slow and require extensive labeling, which hampers timely responses to potential threats. In response, we introduce a groundbreaking approach using filter-array-based hyperspectral imaging technology, enhanced by a super-resolution demosaicking technique. This innovative technology streamlines the detection process and significantly enhances the resolution of mosaic hyperspectral imaging. By utilizing a snapshot hyperspectral camera with a 15 ms integration time, it facilitates the identification of bacteria at the single-cell level without requiring chemical labels. The integration of a 3D convolutional neural network optimizes the recognition of pathogenic bacteria, achieving an impressive accuracy of 91.7%. Our approach dramatically improves the efficiency and effectiveness of bacterial detection, providing a promising solution for critical applications in public health and the food industry.

5-hydroxymethylcytosine sequencing in plasma cell-free DNA identifies unique epigenomic features in prostate cancer patients resistant to androgen deprivation therapies.

Currently, no biomarkers are available to identify resistance to androgen-deprivation therapies (ADT) in men with hormone-naive prostate cancer. Since 5-hydroxymethylcytosines (5hmC) in gene body are associated with gene activation, in this study, we evaluated whether 5hmC signatures in cell-free DNA (cfDNA) predicts early resistance to ADT. We collected a total of 139 serial plasma samples from 55 prostate cancer patients receiving ADT at three time points including baseline (prior to initiating ADT, N=55), 3-month (after initiating ADT, N=55), and disease progression (N=15) within 24 months or 24-month if no progression was detected (N=14). To quantify 5hmC abundance across the genome, we used selective chemical labeling sequencing and mapped sequence reads to individual genes. Differential methylation analysis in baseline samples identified significant 5hmC difference in 1,642 of 23,433 genes between patients with and without progression (false discovery rate, FDR<0.1). Patients with disease progression showed significant 5hmC enrichments in multiple hallmark gene sets with androgen responses as top enriched gene set (FDR=1.19E-13). Interestingly, this enrichment was driven by a subgroup of patients featuring a significant 5hmC hypermethylation in the gene sets involving AR , FOXA1 and GRHL2 . To quantify overall activities of these gene sets, we developed a gene set activity scoring algorithm and observed significant association of high activity scores with poor progression-free survival (P<0.05). Longitudinal analysis showed that the high activity scores were significantly reduced after 3-months of initiating ADT (P<0.0001) but returned to higher levels when the disease was progressed (P<0.05). This study demonstrates that 5hmC-based activity scores from gene sets involved in AR , FOXA1 and GRHL2 may be used as biomarkers to determine early treatment resistance, monitor disease progression, and potentially identify patients who would benefit from upfront treatment intensification.

Mapping Start Codons of Small Open Reading Frames by N-Terminomics Approach

sORF-encoded peptides (SEPs) refer to proteins encoded by small open reading frames (sORFs) with a length of less than 100 amino acids, which play an important role in various life activities. Analysis of known SEPs showed that using non-canonical initiation codons of SEPs was more common. However, the current analysis of SEP sequences mainly relies on bioinformatics prediction, and most of them use AUG as the start site, which may not be completely correct for SEPs. Chemical labeling was used to systematically analyze the N-terminal sequences of SEPs to accurately define the start sites of SEPs. By comparison, we found that dimethylation and guanidinylation are more efficient than acetylation. The ACN precipitation and heating precipitation performed better in SEP enrichment. As an N-terminal peptide enrichment material, Hexadhexaldehyde was superior to CNBr-activated agarose and NHS-activated agarose. Combining these methods, we identified 128 SEPs with 131 N-terminal sequences. Among them, two-thirds are novel N-terminal sequences, and most of them start from the 11-31st amino acids of the original sequence. Partial novel N-termini were produced by proteolysis or signal peptide removal. Some SEPs' transcription start sites were corrected to be non-AUG start codons. One novel start codon was validated using GFP-tag vectors. These results demonstrated that the chemical labeling approaches would be beneficial for identifying the start codons of sORFs and the real N-terminal of their encoded peptides, which helps better understand the characterization of SEPs.

De Novo Synthesis of Perdeuterated Phosphoinositide by Installing a Non-native Phospholipid Biopathway in E. coli.

Phosphatidylinositol (PI) and its phosphorylated derivatives are of paramount importance in cellular functions and diseases. Understanding their diverse roles is, however, challenged by difficulties in synthesis and labeling techniques. In this proof-of-concept study, we demonstrate that PI can be straightforwardly de novo-synthesized and deuterium (2H)-labeled in Escherichia coli by genomic insertion of PI synthase from Trypanosoma brucei under constitutive synthetic promoter proD. Insertion into loci atpi-gidB and ybb revealed PI accumulation of 41% and 34% (mol/mol), respectively, when cultivated with glycerol as the sole carbon source. Growth of the atpi-gidB-PIS strain in deuterium-labeled (2H) substrates D2O, D8-glycerol, and D6-myo-inositol achieved PI deuteration of 90%, PE deuteration of 95%, and total fatty acids|fatty acid (FA) deuteration of 97%. This study offers an alternative convenient route to chemical and enzymatic labeling synthesis of PI; more excitingly, this work also, in principle, opens a door for tailoring the FA profile of deuterated PI/PE for task-specific application by repurposing FA biosynthesis pathways.

Combining Data Independent Acquisition With Spike-In SILAC (DIA-SiS) Improves Proteome Coverage and Quantification

Data-independent acquisition (DIA) is increasingly preferred over data-dependent acquisition due to its higher throughput and fewer missing values. Whereas data-dependent acquisition often uses stable isotope labeling to improve quantification, DIA mostly relies on label-free approaches. Efforts to integrate DIA with isotope labeling include chemical methods like mass differential tags for relative and absolute quantification and dimethyl labeling, which, while effective, complicate sample preparation. Stable isotope labeling by amino acids in cell culture (SILAC) achieves high labeling efficiency through the metabolic incorporation of heavy labels into proteins invivo. However, the need for metabolic incorporation limits the direct use in clinical scenarios and certain high-throughput experiments. Spike-in SILAC (SiS) methods use an externally generated heavy sample as an internal reference, enabling SILAC-based quantification even for samples that cannot be directly labeled. Here, we combine DIA-SiS, leveraging the robust quantification of SILAC without the complexities associated with chemical labeling. We developed DIA-SiS and rigorously assessed its performance with mixed-species benchmark samples on bulk and single cell-like amount level. We demonstrate that DIA-SiS substantially improves proteome coverage and quantification compared to label-free approaches and reduces incorrectly quantified proteins. Additionally, DIA-SiS proves effective in analyzing proteins in low-input formalin-fixed paraffin-embedded tissue sections. DIA-SiS combines the precision of stable isotope-based quantification with the simplicity of label-free sample preparation, facilitating simple, accurate, and comprehensive proteome profiling.

DNA-Directed Activation of Photocatalytic Labeling at Cell-Cell Contact Sites.

Cell-cell interactions govern diverse biological activities, necessitating molecular tools for understanding and regulating these interactions. Photoredox chemistry can detect cell-cell interactions by anchoring photocatalysts on cellular membranes to generate reactive species that tag closely contacting cells. However, the activation of photocatalysts lacks precise spatial resolution for selectively labeling intercellular interfaces. Herein, we report a DNA-based approach to selectively activate photocatalytic reactions at cell-cell contacts. Two cell populations are coated with distinct DNA strands, which interact at intercellular contacts, mediating the site-specific turn-on of a Ru(bpy)3-type photocatalyst. We demonstrate high spatial specificity for intercellular chemical labeling in cultured mammalian cells. Furthermore, as a proof of concept, we activate the dynamic DNA catalyst at cell-cell contacts in response to customized DNA triggers. This study lays the foundation for designing versatile chemical tools with high spatial precision and programmable responsiveness, along with the temporal resolution afforded by photoirradiation, to investigate and manipulate cell-cell interactions.

Chikungunya Virus RNA Secondary Structures Impact Defective Viral Genome Production.

Chikungunya virus (CHIKV) is a mosquito-borne RNA virus that poses an emerging threat to humans. In a manner similar to other RNA viruses, CHIKV encodes an error-prone RNA polymerase which, in addition to producing full-length genomes, gives rise to truncated, non-functional genomes, which have been coined defective viral genomes (DVGs). DVGs have been intensively studied in the context of therapy, as they can inhibit viral replication and dissemination in their hosts. In this work, we interrogate the influence of viral RNA secondary structures on the production of CHIKV DVGs. We experimentally map RNA secondary structures of the CHIKV genome using selective 2'-hydroxyl acylation analyzed by primer extension and mutational profiling (SHAPE-MaP), which couples chemical labelling with next-generation sequencing. We correlate the inferred secondary structure with preferred deletion sites of CHIKV DVGs. We document an increased probability of DVG generation with truncations at unpaired nucleotides within the secondary structure. We then generated a CHIKV mutant bearing synonymous changes at the nucleotide level to disrupt the existing RNA secondary structure (CHIKV-D2S). We show that CHIKV-D2S presents altered DVG generation compared to wild-type virus, correlating with the change in RNA secondary structure obtained by SHAPE-MaP. Our work thus demonstrates that RNA secondary structure impacts CHIKV DVG production during replication.

Lipid- and protein-directed photosensitizer proximity labeling captures the cholesterol interactome.

The physical properties of cellular membranes, including fluidity and function, are influenced by protein and lipid interactions. In situ labeling chemistries, most notably proximity-labeling interactomics are well suited to characterize these dynamic and often fleeting interactions. Established methods require distinct chemistries for proteins and lipids, which limits the scope of such studies. Here we establish a singlet-oxygen-based photocatalytic proximity labeling platform (POCA) that reports intracellular interactomes for both proteins and lipids with tight spatiotemporal resolution using cell-penetrant photosensitizer reagents. Using both physiologically relevant lipoprotein-complexed probe delivery and genetic manipulation of cellular cholesterol handling machinery, cholesterol-directed POCA captured established and unprecedented cholesterol binding proteins, including protein complexes sensitive to intracellular cholesterol levels and proteins uniquely captured by lipoprotein uptake. Protein-directed POCA accurately mapped known intracellular membrane complexes, defined sterol-dependent changes to the non-vesicular cholesterol transport protein interactome, and captured state-dependent changes in the interactome of the cholesterol transport protein Aster-B. More broadly, we find that POCA is a versatile interactomics platform that is straightforward to implement, using the readily available HaloTag system, and fulfills unmet needs in intracellular singlet oxygen-based proximity labeling proteomics. Thus, we expect widespread utility for POCA across a range of interactome applications, spanning imaging to proteomics.

Selective Naked-Eye Detection of Lung Squamous Cell Carcinoma Mediated by lncRNA SOX2OT Targeted Nanoplasmonic Probe.

The application of nanobiotechnology in biomolecule detection can provide fast and accurate tests for diagnosing molecular changing-associated diseases. The use of AuNPs-thiolated probe conjugates has long been considered as an alternative method for the detection of specific DNA/RNA targets. Here, we present a colorimetric direct detection method for the SOX2OT transcript, long noncoding RNAs (lncRNAs), by using a poly guanine tail (G12) as a template for in situ synthesis of gold nanoparticles (AuNPs) without any chemical modification or DNA labeling. We have then developed this proposed detection system based on two complementary sequences of long noncoding RNA SOX2OT with an extra strand of poly G12. Using this method, we were able to differentiate lung squamous cell carcinoma from adenocarcinoma samples. Based on this disclosure, this invention provides a simple visual method to detect specific lncRNA sequences without the need for amplifying the target lncRNA and discriminate squamous cell carcinoma from adenocarcinoma samples. Our invention provides a diagnostic kit to detect RNA by means of direct detection (PCR-free) of the lncRNA by in situ synthesis of AuNPs based on two probes with an extra strand of poly G12.

Label-free SELEX of aptamers for ultra-sensitive electrochemical aptasensor detection of amanitin in wild mushrooms

BackgroundMushroom poisoning poses a significant global health concern, with high morbidity and mortality rates. The primary lethal toxins responsible for this condition are alpha-amanitin (ɑ-AMA) and beta-amanitin (β-AMA). As a promising bio-recognition molecules in biosensors, aptamers, have been broadly used in the field of food detection. However, the current SELEX-based methods for screening aptamers for structurally similar small molecules were limited by the labelling or salt ion induction. In this study, we aimed to develop a novel label-free SELEX strategy for the screening of aptamers with high affinity and constructed new aptasensors for the detection of ɑ-AMA and β-AMA. ResultsA novel label-free SELEX strategy based on the positively charged gold nanoparticles (AuNPs) was proposed to simultaneous screening of aptamers for ɑ-AMA and β-AMA. Only 18 rounds of SELEX were required to obtain new aptamers. The candidate aptamers were analyzed by colloidal gold assay, and the sequences of ɑ-30 and β-37 displayed great affinity with Kd values of 22.26 nM and 23.32 nM, respectively, without interference from botanical toxins. Notably, the truncated aptamers ɑ-30-2 (50 bp) and β-37-2 (57 bp) exhibited higher affinity than their original counterpart (79 bp). Subsequently, the selected aptamers were utilized to construct recognition probes for electrochemical aptasensors based on hairpin cyclic cleavage of substrates by Cu2+ dependent DNAzyme and Exo I-triggered recycling cascades. The detection platform showed excellent analytical performance with limits of detection as low as 4.57 pg/mL (ɑ-AMA) and 8.49 pg/mL (β-AMA). Moreover, the aptasensors exhibited superior performance in mushroom and urine samples. SignificanceThis work developed a simple and efficient label-free SELEX method for screening new aptamers for ɑ-AMA and β-AMA, which employed the positively charged AuNPs as the screening medium, without the need for chemical labelling of libraries or induction of salt ions. Furthermore, two novel electrochemical aptasensors were developed based on our newly obtained aptamers, which offer the new biosensing tool for ultrasensitive detection of the AMA poisoning, showing great potential in practical applications.

Cell-surface Milieu Remodeling in Human Dendritic Cell Activation.

Dendritic cells (DCs) are specialized sentinel and APCs coordinating innate and adaptive immunity. Through proteins on their cell surface, DCs sense changes in the environment, internalize pathogens, present processed Ags, and communicate with other immune cells. By combining chemical labeling and quantitative mass spectrometry, we systematically profiled and compared the cell-surface proteomes of human primary conventional DCs (cDCs) in their resting and activated states. TLR activation by a lipopeptide globally reshaped the cell-surface proteome of cDCs, with >100 proteins upregulated or downregulated. By simultaneously elevating positive regulators and reducing inhibitory signals across multiple protein families, the remodeling creates a cell-surface milieu promoting immune responses. Still, cDCs maintain the stimulatory-to-inhibitory balance by leveraging a distinct set of inhibitory molecules. This analysis thus uncovers the molecular complexity and plasticity of the cDC cell surface and provides a roadmap for understanding cDC activation and signaling.

Rapid Single Step Atmospheric Pressure Plasma Jet Deposition of a SERS Active Surface

Surface-enhanced Raman Spectroscopy (SERS) is a highly sensitive detection technique capable of nanomolar or lower detection limits for some analytes.1-3 The key parameter is control of the surface nanostructure to optimise this remarkable enhancement, providing non-destructive detection without the need for chemical labelling. The bottleneck for the wide applicability of SERS as a valuable analytical tool is twofold: (1) rapid fabrication with the required nanostructure and (2) the difficulty in recovering a baseline before exposure or re-exposure to the target matrix. Here we describe an atmospheric plasma jet method for rapid single-step synthesis of SERS active silver on glass and demonstrate the potential of plasma to remove the adsorbed analyte to recover a baseline.The method described in this study employs an atmospheric pressure plasma jet (APPJ) for rapid single-step deposition of nanostructured silver materials with SERS.4,5 Non-thermal plasmas under reduced pressure offer a unique redox chemistry, partly due to the highly energised electrons and are essential for processing many materials and chemical transformations. Electrochemically, a helium-conducting gas allows various redox reactions to occur, without the need of restricting solvent mediums. An APPJ presents a medium which can be considered an electrode due to the presence of electrons and electrolytes, with the ability to drive reduction processes.6 APPJs allow fascinating chemistry to occur, balancing the thermal kinetic energy distribution between electrons and other neutral and ionised species. Consequently, plasma jets are used for etching, cleaning, and medical treatments, as well as driving highly energised electrons in redox reactions.7-9 The plasma was ignited at a stainless-steel needle electrode tip positioned in a 440 mM I.D. ceramic nozzle, with a plume extending 2 mm from the nozzle tip. Silver deposits were ‘written’ precisely in a 2D regular pattern of plasma deposited silver on borosilicate glass for Raman interrogation without any post-treatment by feeding a silver salt into the APPJ. The APPJ ceramic nozzle prints 125 ± 25 m diameter silver islands with a height of approx. 370 nm, separated by 500 mm, these islands formed the rudimentary SERS substrates.The surface morphology and microstructure through SEM and AFM will be described– assessing how microstructure will correlate to SERS enhancement. The concentration dependence will be quantitatively evaluated using various analytes over a wide range of 1 x 10-7 M to 1 x 10-2 M. The detection limit was calculated using three times the lowest concentration detectable standard deviation, equating to 154 ppb. The particle morphology and SERS enhancement are compared to various commercial substrates. Using the same APPJ system for the deposition of silver metal, a helium plasma doped with 4 % oxygen, followed by a separate treatment of helium doped with 4 % hydrogen, was found effective in restoring the zero baseline Raman response. After the cleaning steps, all analytes could show zero baseline recovery with Raman response regeneration. After successive cycles of application of analyte and then oxygen and hydrogen treatment, there is a slight drop in the SERS signal.4,10 Silver readily oxidises to form silver oxide after exposure to helium plasma doped with oxygen, as confirmed using XRD and XPS. This plasma oxidation causes a change in the microstructure of the particles, ultimately sintering together with successive oxidation cycles.Plasma-prepared substrates show significant gains with respect to the economical use of materials and the rapidity of the synthesis of the substrates. We showcase using the atmospheric pressure plasma jet method for synthesis and baseline recovery as an integral part of an analytical device. This approach presents the prospect of reusing the same SERS device for analysis, which may be a key advantage for academic and industrial applications. 11-13 Figure caption:(a) Raman spectra of R6G with most prominent peak measured at 1651cm-1 after oxygen and hydrogen treatment with the black lines showing the Raman spectra of the surface before application of analyte. (b) The peak intensity at 1586cm-1 peak for 4MBA for each measurement cycle with the analyte and before analyte application (after oxygen and hydrogen treatment) (c) Depicting the cleaning and regeneration of SERS signal on a borosilicate substrate. Both 4MBA and R6G were dissolved in methanol at 1 x 10-4M and drop cast onto the substrate. (d) normal X-ray diffraction spectra of PDS between 5 – 80 o 2θ for the original plasma deposit (i), oxidised plasma clean (ii) and hydrogen plasma clean (iii). All assignment was carried out using the Bruker XRD database, using JCPDS 04-0783 and 43-0997 for Ag and Ag2O, respectively. Figure 1

Chemical Isotope Labeling and Dual-Filtering Strategy for Comprehensive Profiling of Urinary Glucuronide Conjugates.

Glucuronidation, a crucial process in phase II metabolism, plays a vital role in the detoxification and elimination of endogenous substances and xenobiotics. A comprehensive and confident profiling of glucuronate-conjugated metabolites is imperative to understanding their roles in physiological and pathological processes. In this study, a chemical isotope labeling and dual-filtering strategy was developed for global profiling of glucuronide metabolites in biological samples. N,N-Dimethyl ethylenediamine (DMED-d0) and its deuterated counterpart DMED-d6 were used to label carboxylic acids through an amidation reaction. First, carboxyl-containing compounds were extracted based on a characteristic mass difference (Δm/z, 6.037 Da) observed in MS between light- and heavy-labeled metabolites (filter I). Subsequently, within the pool of carboxyl-containing compounds, glucuronides were identified using two pairs of diagnostic ions (m/z 247.1294/253.1665 and 229.1188/235.1559 for DMED-d0/DMED-d6-labeled glucuronides) originating from the fragmentation of the derivatized glucuronic acid group in MS/MS (filter II). Compared with non-derivatization, DEMD labeling significantly enhanced the detection sensitivity of glucuronides, as evidenced by a 3- to 55-fold decrease in limits of detection for representative standards. The strategy was applied to profiling glucuronide metabolites in urine samples from colorectal cancer (CRC) patients. A total of 685 features were screened as potential glucuronides, among which 181 were annotated, mainly including glucuronides derived from lipids, organic oxygen, and phenylpropanoids. Enzymatic biosynthesis was employed to accurately identify unknown glucuronides without standards, demonstrating the reliability of the dual-filtering strategy. Our strategy exhibits great potential for profiling the glucuronide metabolome with high coverage and confidence to reveal changes in CRC and other diseases.

Regioselective analysis of heat-induced conformational changes of β-lactoglobulin by quantitative liquid chromatography–mass spectrometry analysis of chemical labeling kinetics

β-Lactoglobulin is a main allergen in cow's milk; its allergenicity is strongly impacted by processing. To understand heat-induced epitope-specific effects, the present study analyzed regiospecific conformational changes of heated native β-lactoglobulin variant A (BLG-A). Complementary fluorescence spectroscopy methods indicated two denaturation phases comprising minor sequential conformational changes (25–75 °C) and complete transitions (80–90 °C). Regioselective conformational changes of BLG-A in the native state (25 °C), sequential (70 °C) and complete transition (90 °C) were determined by quantitative liquid chromatography–mass spectrometry analysis of chemical labeling kinetics covering 14 lysine residues and the N-terminus. Conformational changes in two phases were observed for N-terminus, K8 (both N-terminal chain), K60 (β-sheet C), K75 (β-sheet D), K77 (DE loop), K83 (β-sheet E), K100 and K101 (FG loop). The residues K14 (β-sheet A1), K47 (β-sheet B), K69, K70 (both β-sheet D), and K91 (β-sheet F) were not involved in conformational changes.

6-Plex Tandem Phosphorus Tags (TPT) for Accurate Quantitative Proteomics.

Isobaric chemical labeling is a widely used strategy for high-throughput quantitative proteomics based on mass spectrometry. However, commercially available reagents have high costs in applications as well as the sensitivity limitations for detection of the trace protein samples. Previously, we developed a 2-plex isobaric labeling strategy based on phosphorus chemistry for ultrasensitive proteome quantification with high accuracy. In this work, 6-plex tandem phosphorus tags (TPT) were developed with 3-fold increase in the multiplexing quantitative capacity compared to the 2-plex isobaric phosphorus reagents introduced previously. High isotope enrichment of 18O labeling was incorporated into the phosphoryl group with three exchangeable oxygen atoms by using commercially available H218O. The combinational incorporations of 18O atom in reporter ions and balance group set up the low-cost foundation for development of multiplex TPT reagents. The novel 6-plex TPT reagents could produce phosphoramidate as unique reporter ions with approximately 1 Da mass difference and thus enable 6-plex quantitative analysis in high-resolution ESI-MS/MS analysis. Using HeLa cell tryptic peptides, we concluded that 6-plex TPT reagents could facilitate large-scale accurate quantitative proteomics with very high labeling efficiency.

Adipose microenvironment promotes hypersialylation of ovarian cancer cells.

Ovarian and other peritoneal cancers have a strong tendency to metastasize into the surrounding adipose tissue. This study describes an effect of the adipose microenvironment on upregulation of sialic acid-containing glycans in ovarian cancer (OC). Heterogeneous populations of glycosylated OC tumors converged to a highly sialylated cell state that regulates tumorigenesis in an immune-dependent manner. We modeled the adipose microenvironment by conditioning growth media with human patient-derived adipose tissue. OC cell lines grown in the presence vs. absence of adipose conditioned media (ACM) were characterized by transcriptomics, western blotting, and chemical biology glycan labeling methods. Fluorescence-activated cell sorting was used to separate adipose-driven upregulation of hypersialylated ("SNA-high") vs. hyposialylated ("SNA-low") OC subpopulations. The two subpopulations were characterized by further transcriptomic and quantitative polymerase chain reaction analyses, then injected into a syngeneic mouse model. Immune system involvement was implicated using wild type and athymic nude mice with a primary endpoint of overall survival. Adipose conditioning resulted in upregulation of sialyltransferases ST3GAL1, ST6GAL1, ST6GALNAC3, and ST8Sia1. In culture, OC cells displayed two distinct sialylated subpopulations that were stable for up to 9 passages, suggesting inherent heterogeneity in sialylation that is maintained throughout cell division and media changes. OC tumors that implanted in the omental adipose tissue exclusively reprogrammed to the highly sialylated subpopulation. In wild type C57BL/6 mice, only the hypersialylated SNA-high subpopulation implanted in the adipose, whereas the hyposialylated SNA-low subpopulation failed to be tumorigenic (p=0.023, n=5). In the single case where SNA-low established a tumor, post-mortem analysis revealed reprogramming of the tumor to the SNA-high state in vivo. In athymic nude mice, both subpopulations rapidly formed tumors, implicating a role of the adaptive immune system. These findings suggest a model of glycan-dependent tumor evolution wherein the adipose microenvironment reprograms OC to a tumorigenic state that resists the adaptive immune system. Mechanistically, adipose factors upregulate sialyltransferases. To our knowledge, this is the first demonstration of the effect of adipose microenvironment on OC tumor sialylation. Our results set the stage for translational applications targeting sialic acid pathways in OC and other peritoneal cancer tumorigenesis and metastasis.

Base-resolution m5C profiling across the mammalian transcriptome by bisulfite-free enzyme-assisted chemical labeling approach

5-methylcytosine (m5C) is a prevalent RNA modification crucial for gene expression regulation. However, accurate and sensitive m5C sites identification remains challenging due to severe RNA degradation and reduced sequence complexity during bisulfite sequencing (BS-seq). Here, we report m5C-TAC-seq, a bisulfite-free approach combining TET-assisted m5C-to-f5C oxidation with selective chemical labeling, therefore enabling direct base-resolution m5C detection through pre-enrichment and C-to-T transitions at m5C sites. With m5C-TAC-seq, we comprehensively profiled the m5C methylomes in human and mouse cells, identifying a substantially larger number of confident m5C sites. Through perturbing potential m5C methyltransferases, we deciphered the responsible enzymes for most m5C sites, including the characterization of NSUN5's involvement in mRNA m5C deposition. Additionally, we characterized m5C dynamics during mESC differentiation. Notably, the mild reaction conditions and preservation of nucleotide composition in m5C-TAC-seq allow m5C detection in chromatin-associated RNAs. The accurate and robust m5C-TAC-seq will advance research into m5C methylation functional investigation.

Quenching Trypsin Is Unnecessary in Filter-Based Bottom-Up Proteomics.

Quenching digestions in proteomics prior to analysis is routine in order to eliminate residual protease activity. Residual activity leads to overdigestion, nonspecific star-activity, and back-exchange in isotopic 18O quantitation. Chemical and isobaric labeling (e.g., TMT/iTRAQ) of proteins or peptides for mass spectrometry-based proteomics is generally incompatible with ubiquitous postdigestion acidification. This necessitates buffer exchange and pH adjustments. We demonstrate that quenching is unnecessary with peptides generated from protein filter-traps, as trypsin activity and intact trypsin are negligible in the eluate from these preparations. Labeling can be directly performed on enzymatic digests from these methods, improving recovery, throughput, and ease of automation.