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Roberts DS, Loo JA, Tsybin YO, Liu X, Wu S, Chamot-Rooke J, Agar JN, Paša-Tolić L, Smith LM, Ge Y. Top-down proteomics. NATURE REVIEWS. METHODS PRIMERS 2024; 4:38. [PMID: 39006170 PMCID: PMC11242913 DOI: 10.1038/s43586-024-00318-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/24/2024] [Indexed: 07/16/2024]
Abstract
Proteoforms, which arise from post-translational modifications, genetic polymorphisms and RNA splice variants, play a pivotal role as drivers in biology. Understanding proteoforms is essential to unravel the intricacies of biological systems and bridge the gap between genotypes and phenotypes. By analysing whole proteins without digestion, top-down proteomics (TDP) provides a holistic view of the proteome and can decipher protein function, uncover disease mechanisms and advance precision medicine. This Primer explores TDP, including the underlying principles, recent advances and an outlook on the future. The experimental section discusses instrumentation, sample preparation, intact protein separation, tandem mass spectrometry techniques and data collection. The results section looks at how to decipher raw data, visualize intact protein spectra and unravel data analysis. Additionally, proteoform identification, characterization and quantification are summarized, alongside approaches for statistical analysis. Various applications are described, including the human proteoform project and biomedical, biopharmaceutical and clinical sciences. These are complemented by discussions on measurement reproducibility, limitations and a forward-looking perspective that outlines areas where the field can advance, including potential future applications.
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Affiliation(s)
- David S Roberts
- Department of Chemistry, Stanford University, Stanford, CA, USA
- Sarafan ChEM-H, Stanford University, Stanford, CA, USA
| | - Joseph A Loo
- Department of Chemistry and Biochemistry, Department of Biological Chemistry, University of California - Los Angeles, Los Angeles, CA, USA
| | | | - Xiaowen Liu
- Deming Department of Medicine, School of Medicine, Tulane University, New Orleans, LA, USA
| | - Si Wu
- Department of Chemistry and Biochemistry, The University of Alabama, Tuscaloosa, AL, USA
| | | | - Jeffrey N Agar
- Departments of Chemistry and Chemical Biology and Pharmaceutical Sciences, Northeastern University, Boston, MA, USA
| | - Ljiljana Paša-Tolić
- Environmental and Molecular Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Lloyd M Smith
- Department of Chemistry, University of Wisconsin, Madison, WI, USA
| | - Ying Ge
- Department of Chemistry, University of Wisconsin, Madison, WI, USA
- Department of Cell and Regenerative Biology, Human Proteomics Program, University of Wisconsin - Madison, Madison, WI, USA
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Dunham SD, Brodbelt JS. Enhancing Top-Down Analysis of Proteins by Combining Ultraviolet Photodissociation (UVPD), Proton-Transfer Charge Reduction (PTCR), and Gas-Phase Fractionation to Alleviate the Impact of Nondissociated Precursor Ions. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024; 35:255-265. [PMID: 38150423 DOI: 10.1021/jasms.3c00351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2023]
Abstract
Recent advances in top-down mass spectrometry strategies continue to improve the analysis of intact proteins. 193 nm ultraviolet photodissociation (UVPD) is one method well-suited for top-down analysis. UVPD is often performed using relatively low photon flux in order to limit multiple-generation dissociation of fragment ions and maximize sequence coverage. Consequently, a large portion of the precursor ion survives the UVPD process, dominates the spectrum, and may impede identification of fragment ions. Here, we explore the isolation of subpopulations of fragment ions lower and higher than the precursor ion after UVPD as a means to eliminate the impact of the surviving precursor ion on the detection of low abundance fragment ions. This gas-phase fractionation method improved sequence coverage harvested from fragment ions found in the m/z regions lower and higher than the precursor by an average factor of 1.3 and 2.3, respectively. Combining this gas-phase fractionation method with proton transfer charge reduction (PTCR) further increased the sequence coverage obtained from these m/z regions by another factor of 1.3 and 1.4, respectively. Implementing a post-UVPD fractionation + PTCR strategy with six fractionation events resulted in a sequence coverage of 75% for enolase, the highest reported for 193 nm UVPD.
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Affiliation(s)
- Sean D Dunham
- Department of Chemistry, University of Texas, Austin, Texas 787812, United States
| | - Jennifer S Brodbelt
- Department of Chemistry, University of Texas, Austin, Texas 787812, United States
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Zemaitis KJ, Zhou M, Kew W, Paša-Tolić L. 193 nm Ultraviolet Photodissociation for the Characterization of Singly Charged Proteoforms Generated by MALDI. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2023; 34:328-332. [PMID: 36622763 PMCID: PMC10084724 DOI: 10.1021/jasms.2c00302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
MALDI imaging allows for the near-cellular profiling of proteoforms directly from microbial, plant, and mammalian samples. Despite detecting hundreds of proteoforms, identification of unknowns with only intact mass information remains a distinct challenge, even with high mass resolving power and mass accuracy. To this end, many supplementary methods have been used to create experimental databases for accurate mass matching, including bulk or spatially resolved bottom-up and/or top-down proteomics. Herein, we describe the application of 193 nm ultraviolet photodissociation (UVPD) for fragmentation of quadrupole isolated singly charged ubiquitin (m/z 8565) by MALDI-UVPD on a UHMR HF Orbitrap. This platform permitted the high-resolution accurate mass measurement of not just terminal fragments but also large internal fragments. The outlined workflow demonstrates the feasibility of top-down analyses of isolated MALDI protein ions and the potential toward more comprehensive characterization of proteoforms in MALDI imaging applications.
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Affiliation(s)
- Kevin J Zemaitis
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Mowei Zhou
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - William Kew
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Ljiljana Paša-Tolić
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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Dunham SD, Wei B, Lantz C, Loo JA, Brodbelt JS. Impact of Internal Fragments on Top-Down Analysis of Intact Proteins by 193 nm UVPD. J Proteome Res 2023; 22:170-181. [PMID: 36503236 DOI: 10.1021/acs.jproteome.2c00583] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
193 nm ultraviolet photodissociation (UVPD) allows high sequence coverage to be obtained for intact proteins using terminal fragments alone. However, internal fragments, those that contain neither N- nor C- terminus, are typically ignored, neglecting their potential to bolster characterization of intact proteins. Here, we explore internal fragments generated by 193 nm UVPD for proteins ranging in size from 17-47 kDa and using the ClipsMS algorithm to facilitate searches for internal fragments. Internal fragments were only retained if identified in multiple replicates in order to reduce spurious assignments and to explore the reproducibility of internal fragments generated by UVPD. Inclusion of internal fragment improved sequence coverage by an average of 18% and 32% for UVPD and HCD, respectively, across all proteins and charge states studied. However, only an average of 18% of UVPD internal fragments were identified in two out of three replicates relative to the average number identified across all replicates for all proteins studied. Conversely, for HCD, an average of 63% of internal fragments were retained across replicates. These trends reflect an increased risk of false-positive identifications and a need for caution when considering internal fragments for UVPD. Additionally, proton-transfer charge reduction (PTCR) reactions were performed following UVPD or HCD to assess the impact on internal fragment identifications, allowing up to 20% more fragment ions to be retained across multiple replicates. At this time, it is difficult to recommend the inclusion of the internal fragment when searching UVPD spectra without further work to develop strategies for reducing the possibilities of false-positive identifications. All mass spectra are available in the public repository jPOST with the accession number JPST001885.
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Affiliation(s)
- Sean D Dunham
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Benqian Wei
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California 90095, United States
| | - Carter Lantz
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California 90095, United States
| | - Joseph A Loo
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California 90095, United States
| | - Jennifer S Brodbelt
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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