Histone Sample Preparation for Bottom-Up Mass Spectrometry: A Roadmap to Informed Decisions.
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ABSTRACT:
SUBMITTER: Daled S
PROVIDER: S-EPMC8167631 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:we aimed to provide an objective roadmap for histone sample preparation wherein the most notable findings and most important metrics were highlighted. This roadmap included a Histone Coverage Tool that allows researchers to make a snapshot of public or in-house data in search of a protocol that suits their specific needs. However, despite the fact that the coverage provided by a sample preparation workflow is pivotal to answer specific research questions, it should be noted that other metrics such as enzyme specificity and workflow variability can be equally important. Moreover, when it comes to histone sample preparation there are multiple additional challenges and pitfalls compared to regular bottom-up proteomics workflows. First there is the abundance and unequal distribution of arginine and lysine cleavage sites, which makes it virtually impossible to cover the entire histone code with a single bottom-up workflow. The most widely spread workaround for the abundance of cleavage sites is derivatization of lysine residues used to block tryptic digest and create longer peptides. However, this also introduces chemical noise, which obscures biological PTMs, while lowering sensitivity due to diluted signal. The most obvious alternative is an arginine specific digest. However, on the one hand, derivatization of lysine residues not only increases peptide length but also increases retention on the LC-system, while decreasing charge state distribution of the precursor ions. The latter presumably reduces instrumental variation of the workflow, which is remarkable since this source of variation is generally assumed to be constant in the field of LC-MS/MS based proteomics. On the other hand, lysine derivatization also increases the singly charged precursor fraction, which is usually not fragmented in regular data dependent acquisitions, thus increasing the risk of losing annotations. It is clear that not one histone sample preparation workflow will fit all research questions. However, we hope that this manuscript will guide researchers in making informed decisions about the many pitfalls and trade-offs involved in optimizing or assessing histone sample preparation workflows.
2021-04-27 | PXD024423 | Pride
Project description:Despite their important role in regulating gene expression, posttranslational histone modifications remain technically challenging to analyze. For identification by bottom-up MS, propionylation is required prior to and following trypsin digestion. Hereby, more hydrophobic peptides are generated enabling RP HPLC separation. When histone dynamics are studied in a quantitative manner, specificity, and efficiency of this chemical derivatization are crucial. Therefore we examined eight different protocols, including two different propionylation reagents. This revealed amidation (up to 70%) and methylation (up to 9%) of carboxyl groups as a side reaction. Moreover, incomplete (up to 85%) as well as a specific propionylation (up to 63%) can occur, depending on the protocol. These results highlight the possible pitfalls and implications for data analysis when doing bottom-up MS on histones.
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Project description:Hydrogen-deuterium exchange mass spectrometry is an important method for protein structure-function analysis. The bottom-up approach uses protein digestion to localize deuteration to higher resolution, and the essential measurement involves centroid mass determinations on a very large set of peptides. In the course of evaluating systems for various projects, we established two (HDX-MS) platforms that consisted of a FT-MS and a high-resolution QTOF mass spectrometer, each with matched front-end fluidic systems. Digests of proteins spanning a 20-110 kDa range were deuterated to equilibrium, and figures-of-merit for a typical bottom-up (HDX-MS) experiment were compared for each platform. The Orbitrap Velos identified 64% more peptides than the 5600 QTOF, with a 42% overlap between the two systems, independent of protein size. Precision in deuterium measurements using the Orbitrap marginally exceeded that of the QTOF, depending on the Orbitrap resolution setting. However, the unique nature of FT-MS data generates situations where deuteration measurements can be inaccurate, because of destructive interference arising from mismatches in elemental mass defects. This is shown through the analysis of the peptides common to both platforms, where deuteration values can be as low as 35% of the expected values, depending on FT-MS resolution, peptide length and charge state. These findings are supported by simulations of Orbitrap transients, and highlight that caution should be exercised in deriving centroid mass values from FT transients that do not support baseline separation of the full isotopic composition.
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Project description:For mass spectrometry-based proteomics, the selected sample preparation strategy is a key determinant for information that will be obtained. However, the corresponding selection is often not based on a fit-for-purpose evaluation. Here we report a comparison of in-gel (IGD), in-solution (ISD), on-filter (OFD), and on-pellet digestion (OPD) workflows on the basis of targeted (QconCAT-multiple reaction monitoring (MRM) method for mitochondrial proteins) and discovery proteomics (data-dependent acquisition, DDA) analyses using three different human head and neck tissues (i.e., nasal polyps, parotid gland, and palatine tonsils). Our study reveals differences between the sample preparation methods, for example, with respect to protein and peptide losses, quantification variability, protocol-induced methionine oxidation, and asparagine/glutamine deamidation as well as identification of cysteine-containing peptides. However, none of the methods performed best for all types of tissues, which argues against the existence of a universal sample preparation method for proteome analysis.
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Project description:Xenopus laevis is an important model organism in developmental biology. While there is a large literature on changes in the organism's transcriptome during development, the study of its proteome is at an embryonic state. Several papers have been published recently that characterize the proteome of X. laevis eggs and early-stage embryos; however, proteomic sample preparation optimizations have not been reported. Sample preparation is challenging because a large fraction (~90 % by weight) of the egg or early-stage embryo is yolk. We compared three common protein extraction buffer systems, mammalian Cell-PE LB(TM) lysing buffer (NP40), sodium dodecyl sulfate (SDS), and 8 M urea, in terms of protein extraction efficiency and protein identifications. SDS extracts contained the highest concentration of proteins, but this extract was dominated by a high concentration of yolk proteins. In contrast, NP40 extracts contained ~30 % of the protein concentration as SDS extracts, but excelled in discriminating against yolk proteins, which resulted in more protein and peptide identifications. We then compared digestion methods using both SDS and NP40 extraction methods with one-dimensional reverse-phase liquid chromatography-tandem mass spectrometry (RPLC-MS/MS). NP40 coupled to a filter-aided sample preparation (FASP) procedure produced nearly twice the number of protein and peptide identifications compared to alternatives. When NP40-FASP samples were subjected to two-dimensional RPLC-ESI-MS/MS, a total of 5171 proteins and 38,885 peptides were identified from a single stage of embryos (stage 2), increasing the number of protein identifications by 23 % in comparison to other traditional protein extraction methods.
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