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Wang CR, McFarlane LO, Pukala TL. Exploring snake venoms beyond the primary sequence: From proteoforms to protein-protein interactions. Toxicon 2024; 247:107841. [PMID: 38950738 DOI: 10.1016/j.toxicon.2024.107841] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2024] [Revised: 06/26/2024] [Accepted: 06/28/2024] [Indexed: 07/03/2024]
Abstract
Snakebite envenomation has been a long-standing global issue that is difficult to treat, largely owing to the flawed nature of current immunoglobulin-based antivenom therapy and the complexity of snake venoms as sophisticated mixtures of bioactive proteins and peptides. Comprehensive characterisation of venom compositions is essential to better understanding snake venom toxicity and inform effective and rationally designed antivenoms. Additionally, a greater understanding of snake venom composition will likely unearth novel biologically active proteins and peptides that have promising therapeutic or biotechnological applications. While a bottom-up proteomic workflow has been the main approach for cataloguing snake venom compositions at the toxin family level, it is unable to capture snake venom heterogeneity in the form of protein isoforms and higher-order protein interactions that are important in driving venom toxicity but remain underexplored. This review aims to highlight the importance of understanding snake venom heterogeneity beyond the primary sequence, in the form of post-translational modifications that give rise to different proteoforms and the myriad of higher-order protein complexes in snake venoms. We focus on current top-down proteomic workflows to identify snake venom proteoforms and further discuss alternative or novel separation, instrumentation, and data processing strategies that may improve proteoform identification. The current higher-order structural characterisation techniques implemented for snake venom proteins are also discussed; we emphasise the need for complementary and higher resolution structural bioanalytical techniques such as mass spectrometry-based approaches, X-ray crystallography and cryogenic electron microscopy, to elucidate poorly characterised tertiary and quaternary protein structures. We envisage that the expansion of the snake venom characterisation "toolbox" with top-down proteomics and high-resolution protein structure determination techniques will be pivotal in advancing structural understanding of snake venoms towards the development of improved therapeutic and biotechnology applications.
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Affiliation(s)
- C Ruth Wang
- Discipline of Chemistry, School of Physics, Chemistry and Earth Sciences, The University of Adelaide, Adelaide, 5005, Australia
| | - Lewis O McFarlane
- Discipline of Chemistry, School of Physics, Chemistry and Earth Sciences, The University of Adelaide, Adelaide, 5005, Australia
| | - Tara L Pukala
- Discipline of Chemistry, School of Physics, Chemistry and Earth Sciences, The University of Adelaide, Adelaide, 5005, Australia.
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2
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Du G, Healy LB, David L, Walker C, El-Baba TJ, Lutomski CA, Goh B, Gu B, Pi X, Devant P, Fontana P, Dong Y, Ma X, Miao R, Balasubramanian A, Puthenveetil R, Banerjee A, Luo HR, Kagan JC, Oh SF, Robinson CV, Lieberman J, Wu H. ROS-dependent S-palmitoylation activates cleaved and intact gasdermin D. Nature 2024; 630:437-446. [PMID: 38599239 DOI: 10.1038/s41586-024-07373-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Accepted: 04/02/2024] [Indexed: 04/12/2024]
Abstract
Gasdermin D (GSDMD) is the common effector for cytokine secretion and pyroptosis downstream of inflammasome activation and was previously shown to form large transmembrane pores after cleavage by inflammatory caspases to generate the GSDMD N-terminal domain (GSDMD-NT)1-10. Here we report that GSDMD Cys191 is S-palmitoylated and that palmitoylation is required for pore formation. S-palmitoylation, which does not affect GSDMD cleavage, is augmented by mitochondria-generated reactive oxygen species (ROS). Cleavage-deficient GSDMD (D275A) is also palmitoylated after inflammasome stimulation or treatment with ROS activators and causes pyroptosis, although less efficiently than palmitoylated GSDMD-NT. Palmitoylated, but not unpalmitoylated, full-length GSDMD induces liposome leakage and forms a pore similar in structure to GSDMD-NT pores shown by cryogenic electron microscopy. ZDHHC5 and ZDHHC9 are the major palmitoyltransferases that mediate GSDMD palmitoylation, and their expression is upregulated by inflammasome activation and ROS. The other human gasdermins are also palmitoylated at their N termini. These data challenge the concept that cleavage is the only trigger for GSDMD activation. They suggest that reversible palmitoylation is a checkpoint for pore formation by both GSDMD-NT and intact GSDMD that functions as a general switch for the activation of this pore-forming family.
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Affiliation(s)
- Gang Du
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA.
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA.
| | - Liam B Healy
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
| | - Liron David
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA.
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA.
- Seqirus, Cambridge, MA, USA.
| | - Caitlin Walker
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Life Sciences, Ben-Gurion University of the Negev, Be'er Sheva, Israel
| | - Tarick J El-Baba
- Department of Chemistry, University of Oxford, Oxford, UK
- Kavli Institute for NanoScience Discovery, University of Oxford, Oxford, UK
| | - Corinne A Lutomski
- Department of Chemistry, University of Oxford, Oxford, UK
- Kavli Institute for NanoScience Discovery, University of Oxford, Oxford, UK
| | - Byoungsook Goh
- Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Boston, MA, USA
| | - Bowen Gu
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Pediatrics, Harvard Medical School, Boston, MA, USA
| | - Xiong Pi
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
| | - Pascal Devant
- Harvard Medical School and Division of Gastroenterology, Boston Children's Hospital, Boston, MA, USA
| | - Pietro Fontana
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
| | - Ying Dong
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
| | - Xiyu Ma
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Pediatrics, Harvard Medical School, Boston, MA, USA
| | - Rui Miao
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Pediatrics, Harvard Medical School, Boston, MA, USA
| | - Arumugam Balasubramanian
- Department of Pathology, Dana-Farber/Harvard Cancer Center, Harvard Medical School, Boston, MA, USA
- Department of Laboratory Medicine, Boston Children's Hospital, Boston, MA, USA
| | - Robbins Puthenveetil
- Section on Structural and Chemical Biology, Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Anirban Banerjee
- Section on Structural and Chemical Biology, Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Hongbo R Luo
- Department of Pathology, Dana-Farber/Harvard Cancer Center, Harvard Medical School, Boston, MA, USA
- Department of Laboratory Medicine, Boston Children's Hospital, Boston, MA, USA
| | - Jonathan C Kagan
- Harvard Medical School and Division of Gastroenterology, Boston Children's Hospital, Boston, MA, USA
| | - Sungwhan F Oh
- Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Boston, MA, USA
| | - Carol V Robinson
- Department of Chemistry, University of Oxford, Oxford, UK
- Kavli Institute for NanoScience Discovery, University of Oxford, Oxford, UK
| | - Judy Lieberman
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA
- Department of Pediatrics, Harvard Medical School, Boston, MA, USA
| | - Hao Wu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA.
- Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA.
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Ivanov DG, Cheung K, Kaltashov IA. Probing the Architecture of Multisubunit Protein Complexes with In-line Disulfide Reduction and Native MS Analysis. Anal Chem 2024; 96:8243-8248. [PMID: 38733603 DOI: 10.1021/acs.analchem.4c00879] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2024]
Abstract
Native mass spectrometry (MS) continues to enjoy growing popularity as a means of providing a wealth of information on noncovalent biopolymer assemblies ranging from composition and binding stoichiometry to characterization of the topology of these assemblies. The latter frequently relies on supplementing MS measurements with limited fragmentation of the noncovalent complexes in the gas phase to identify the pairs of neighboring subunits. While this approach has met with much success in the past two decades, its implementation remains difficult (and the success record relatively modest) within one class of noncovalent assemblies: protein complexes in which at least one binding partner has multiple subunits cross-linked by disulfide bonds. We approach this problem by inducing chemical reduction of disulfide bonds under nondenaturing conditions in solution followed by native MS analysis with online buffer exchange to remove unconsumed reagents that are incompatible with the electrospray ionization process. While this approach works well with systems comprised of thiol-linked subunits that remain stable upon reduction of the disulfide bridges (such as immunoglobulins), chemical reduction frequently gives rise to species that are unstable (prone to aggregation). This problem is circumvented by taking advantage of the recently introduced cross-path reactive chromatography platform (XPRC), which allows the disulfide reduction to be carried out in-line, thereby minimizing the loss of metastable protein subunits and their noncovalent complexes with the binding partners prior to MS analysis. The feasibility of this approach is demonstrated using hemoglobin complexes with haptoglobin 1-1, a glycoprotein consisting of four polypeptide chains cross-linked by disulfide bonds.
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Affiliation(s)
- Daniil G Ivanov
- Department of Chemistry, University of Massachusetts─Amherst, Amherst, Massachusetts 01002, United States
| | - Kevin Cheung
- Department of Chemistry, University of Massachusetts─Amherst, Amherst, Massachusetts 01002, United States
| | - Igor A Kaltashov
- Department of Chemistry, University of Massachusetts─Amherst, Amherst, Massachusetts 01002, United States
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Coorssen JR, Padula MP. Proteomics-The State of the Field: The Definition and Analysis of Proteomes Should Be Based in Reality, Not Convenience. Proteomes 2024; 12:14. [PMID: 38651373 PMCID: PMC11036260 DOI: 10.3390/proteomes12020014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2024] [Revised: 04/17/2024] [Accepted: 04/17/2024] [Indexed: 04/25/2024] Open
Abstract
With growing recognition and acknowledgement of the genuine complexity of proteomes, we are finally entering the post-proteogenomic era. Routine assessment of proteomes as inferred correlates of gene sequences (i.e., canonical 'proteins') cannot provide the necessary critical analysis of systems-level biology that is needed to understand underlying molecular mechanisms and pathways or identify the most selective biomarkers and therapeutic targets. These critical requirements demand the analysis of proteomes at the level of proteoforms/protein species, the actual active molecular players. Currently, only highly refined integrated or integrative top-down proteomics (iTDP) enables the analytical depth necessary to provide routine, comprehensive, and quantitative proteome assessments across the widest range of proteoforms inherent to native systems. Here we provide a broad perspective of the field, taking in historical and current realities, to establish a more balanced understanding of where the field has come from (in particular during the ten years since Proteomes was launched), current issues, and how things likely need to proceed if necessary deep proteome analyses are to succeed. We base this in our firm belief that the best proteomic analyses reflect, as closely as possible, the native sample at the moment of sampling. We also seek to emphasise that this and future analytical approaches are likely best based on the broad recognition and exploitation of the complementarity of currently successful approaches. This also emphasises the need to continuously evaluate and further optimize established approaches, to avoid complacency in thinking and expectations but also to promote the critical and careful development and introduction of new approaches, most notably those that address proteoforms. Above all, we wish to emphasise that a rigorous focus on analytical quality must override current thinking that largely values analytical speed; the latter would certainly be nice, if only proteoforms could thus be effectively, routinely, and quantitatively assessed. Alas, proteomes are composed of proteoforms, not molecular species that can be amplified or that directly mirror genes (i.e., 'canonical'). The problem is hard, and we must accept and address it as such, but the payoff in playing this longer game of rigorous deep proteome analyses is the promise of far more selective biomarkers, drug targets, and truly personalised or even individualised medicine.
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Affiliation(s)
- Jens R. Coorssen
- Department of Biological Sciences, Faculty of Mathematics and Science, Brock University, St. Catharines, ON L2S 3A1, Canada
- Institute for Globally Distributed Open Research and Education (IGDORE), St. Catharines, ON L2N 4X2, Canada
| | - Matthew P. Padula
- School of Life Sciences and Proteomics, Lipidomics and Metabolomics Core Facility, Faculty of Science, University of Technology Sydney, Sydney, NSW 2007, Australia
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5
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Huang CF, Kline JT, Negrão F, Robey MT, Toby TK, Durbin KR, Fellers RT, Friedewald JJ, Levitsky J, Abecassis MMI, Melani RD, Kelleher NL, Fornelli L. Targeted Quantification of Proteoforms in Complex Samples by Proteoform Reaction Monitoring. Anal Chem 2024; 96:3578-3586. [PMID: 38354049 PMCID: PMC11008684 DOI: 10.1021/acs.analchem.3c05578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2024]
Abstract
Existing mass spectrometric assays used for sensitive and specific measurements of target proteins across multiple samples, such as selected/multiple reaction monitoring (SRM/MRM) or parallel reaction monitoring (PRM), are peptide-based methods for bottom-up proteomics. Here, we describe an approach based on the principle of PRM for the measurement of intact proteoforms by targeted top-down proteomics, termed proteoform reaction monitoring (PfRM). We explore the ability of our method to circumvent traditional limitations of top-down proteomics, such as sensitivity and reproducibility. We also introduce a new software program, Proteoform Finder (part of ProSight Native), specifically designed for the easy analysis of PfRM data. PfRM was initially benchmarked by quantifying three standard proteins. The linearity of the assay was shown over almost 3 orders of magnitude in the femtomole range, with limits of detection and quantification in the low femtomolar range. We later applied our multiplexed PfRM assay to complex samples to quantify biomarker candidates in peripheral blood mononuclear cells (PBMCs) from liver-transplanted patients, suggesting their possible translational applications. These results demonstrate that PfRM has the potential to contribute to the accurate quantification of protein biomarkers for diagnostic purposes and to improve our understanding of disease etiology at the proteoform level.
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Affiliation(s)
- Che-Fan Huang
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, Illinois 60208, United States
| | - Jake T Kline
- School of Biological Sciences, University of Oklahoma, Norman, Oklahoma 73019, United States
| | - Fernanda Negrão
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, Illinois 60208, United States
| | - Matthew T Robey
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, Illinois 60208, United States
- Proteinaceous, Inc., Evanston, Illinois 60201, United States
| | - Timothy K Toby
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, Illinois 60208, United States
| | - Kenneth R Durbin
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, Illinois 60208, United States
- Proteinaceous, Inc., Evanston, Illinois 60201, United States
| | - Ryan T Fellers
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, Illinois 60208, United States
- Proteinaceous, Inc., Evanston, Illinois 60201, United States
| | - John J Friedewald
- Comprehensive Transplant Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, United States
| | - Josh Levitsky
- Comprehensive Transplant Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, United States
| | - Michael M I Abecassis
- Comprehensive Transplant Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, United States
| | - Rafael D Melani
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, Illinois 60208, United States
| | - Neil L Kelleher
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, Illinois 60208, United States
| | - Luca Fornelli
- School of Biological Sciences, University of Oklahoma, Norman, Oklahoma 73019, United States
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, United States
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6
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Lanzillotti MB, Brodbelt JS. A High-Throughput Workflow for Mass Spectrometry Analysis of Nucleic Acids by Nanoflow Desalting. Anal Chem 2024. [PMID: 38330443 DOI: 10.1021/acs.analchem.3c05428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2024]
Abstract
Broad interest in nucleic acids, both their therapeutic capabilities and understanding the nuances of their structure and resulting function, has increased in recent years. Post-transcriptional modifications, in particular, have become an important analysis target, as these covalent modifications to the sugars, nitrogenous bases, and phosphate backbone impart differential functionality to synthetic and biological nucleic acids. Characterizing these post-transcriptional modifications can be difficult with traditional sequencing workflows; however, advancements in top-down mass spectrometry address these challenges. Online desalting platforms have enabled facile sample cleanup and reliable ionization of increasingly large (100 nt) oligonucleotides, and application of existing tandem mass spectrometry techniques has yielded information-rich spectra which can be used to interrogate primary sequences. To extend the capabilities of top-down MS and its analysis of nucleic acids, we have developed a nanoflow desalting platform for high-throughput and low sample-use desalting coupled with collision-induced dissociation (CID), 213 nm ultraviolet photodissociation (UVPD), and activated-ion electron photodetachment dissociation (a-EPD) to yield high-quality MS/MS spectra. Fragments identified using an m/z-domain isotope matching strategy yielded high sequence coverage (>70%) of a yeast phenylalanine tRNA.
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Affiliation(s)
- Michael B Lanzillotti
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Jennifer S Brodbelt
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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McGee JP, Su P, Durbin KR, Hollas MAR, Bateman NW, Maxwell GL, Conrads TP, Fellers RT, Melani RD, Camarillo JM, Kafader JO, Kelleher NL. Automated imaging and identification of proteoforms directly from ovarian cancer tissue. Nat Commun 2023; 14:6478. [PMID: 37838706 PMCID: PMC10576781 DOI: 10.1038/s41467-023-42208-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Accepted: 09/28/2023] [Indexed: 10/16/2023] Open
Abstract
The molecular identification of tissue proteoforms by top-down mass spectrometry (TDMS) is significantly limited by throughput and dynamic range. We introduce AutoPiMS, a single-ion MS based multiplexed workflow for top-down tandem MS (MS2) directly from tissue microenvironments in a semi-automated manner. AutoPiMS directly off human ovarian cancer sections allowed for MS2 identification of 73 proteoforms up to 54 kDa at a rate of <1 min per proteoform. AutoPiMS is directly interfaced with multifaceted proteoform imaging MS data modalities for the identification of proteoform signatures in tumor and stromal regions in ovarian cancer biopsies. From a total of ~1000 proteoforms detected by region-of-interest label-free quantitation, we discover 303 differential proteoforms in stroma versus tumor from the same patient. 14 of the top proteoform signatures are corroborated by MSI at 20 micron resolution including the differential localization of methylated forms of CRIP1, indicating the importance of proteoform-enabled spatial biology in ovarian cancer.
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Affiliation(s)
- John P McGee
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, IL, USA
| | - Pei Su
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, IL, USA
| | | | | | - Nicholas W Bateman
- Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc, Bethesda, MD, USA
- Department of Gynecologic Surgery and Obstetrics and the Gynecologic Cancer Center of Excellence, John P. Murtha Cancer Center, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - G Larry Maxwell
- Department of Gynecologic Surgery and Obstetrics and the Gynecologic Cancer Center of Excellence, John P. Murtha Cancer Center, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
- Women's Health Integrated Research Center, Inova Women's Service Line, Inova Health System, Falls Church, VA, USA
| | - Thomas P Conrads
- Department of Gynecologic Surgery and Obstetrics and the Gynecologic Cancer Center of Excellence, John P. Murtha Cancer Center, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
- Women's Health Integrated Research Center, Inova Women's Service Line, Inova Health System, Falls Church, VA, USA
| | | | - Rafael D Melani
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, IL, USA
| | - Jeannie M Camarillo
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, IL, USA
- Department of Biochemistry and Molecular Genetics, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Jared O Kafader
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, IL, USA
- Department of Biochemistry and Molecular Genetics, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Neil L Kelleher
- Departments of Molecular Biosciences, Chemistry, and the Feinberg School of Medicine, Northwestern University, Evanston, IL, USA.
- Proteomics Center of Excellence, Evanston, IL, USA.
- Department of Biochemistry and Molecular Genetics, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
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