1
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Crawford SA, Groegler J, Dang M, Michel C, Powell RL, Hohenstein AC, Reyes K, Haskins K, Wiles TA, Delong T. Hybrid insulin peptide isomers spontaneously form in pancreatic beta-cells from an aspartic anhydride intermediate. J Biol Chem 2023; 299:105264. [PMID: 37734557 PMCID: PMC10590738 DOI: 10.1016/j.jbc.2023.105264] [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: 04/21/2023] [Revised: 09/05/2023] [Accepted: 09/13/2023] [Indexed: 09/23/2023] Open
Abstract
Hybrid insulin peptides (HIPs) form in beta-cells when insulin fragments link to other peptides through a peptide bond. HIPs contain nongenomic amino acid sequences and have been identified as targets for autoreactive T cells in type 1 diabetes. A subgroup of HIPs, in which N-terminal amine groups of various peptides are linked to aspartic acid residues of insulin C-peptide, was detected through mass spectrometry in pancreatic islets. Here, we investigate a novel mechanism that leads to the formation of these HIPs in human and murine islets. Our research herein shows that these HIPs form spontaneously in beta-cells through a mechanism involving an aspartic anhydride intermediate. This mechanism leads to the formation of a regular HIP containing a standard peptide bond as well as a HIP-isomer containing an isopeptide bond by linkage to the carboxylic acid side chain of the aspartic acid residue. We used mass spectrometric analyses to confirm the presence of both HIP isomers in islets, thereby validating the occurrence of this novel reaction mechanism in beta-cells. The spontaneous formation of new peptide bonds within cells may lead to the development of neoepitopes that contribute to the pathogenesis of type 1 diabetes as well as other autoimmune diseases.
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Affiliation(s)
- Samantha A Crawford
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Jason Groegler
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Mylinh Dang
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Cole Michel
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Roger L Powell
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Anita C Hohenstein
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA; Department of Immunology and Microbiology, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Kaitlin Reyes
- Department of Immunology and Microbiology, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Kathryn Haskins
- Department of Immunology and Microbiology, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Timothy A Wiles
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Thomas Delong
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.
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2
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Zhong J, Yuan C, Liu L, Du Y, Hui Y, Chen Z, Diao C, Yang R, Liu G, Liu X. PCMT1 regulates the migration, invasion, and apoptosis of prostate cancer through modulating the PI3K/AKT/GSK-3β pathway. Aging (Albany NY) 2023; 15:11654-11671. [PMID: 37899170 PMCID: PMC10637816 DOI: 10.18632/aging.205152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 09/26/2023] [Indexed: 10/31/2023]
Abstract
Protein L-isoaspartate (D-aspartate) O-methyltransferase (PCMT1) is a repair enzyme that catalyzes the conversion of isomerized aspartic acid (iso-Asp) residues into their normal structure, thereby restoring the configuration and function of proteins. Studies have shown that PCMT1 is overexpressed in several tumors and affects patients' prognosis. However, there are few reports on the role of PCMT1 in prostate cancer (PCa). In the present research, with the assistance of The Cancer Genome Atlas Program (TCGA) database, we found that PCMT1 was overexpressed in PCa tissues. The results of quantitative reverse transcription-polymerase chain reaction (qRT-PCR), western blot and immunohistochemistry staining also showed that PCMT1 expression was significantly increased in PCa tissues and cell lines. In PCa clinical samples, PCMT1 expression was closely related to Gleason score, clinical stage, lymph node metastasis and bone metastasis. The experiments of overexpression and knockdown of PCMT1 in vitro or in vivo showed that PCMT1 can significantly promote the proliferation, migration and invasion of PCa cells, inhibit cell apoptosis, and promote the growth of PCa. We furthermore confirmed that PCMT1 regulated the migration, invasion and apoptosis of PCa cells by modulating the phosphatidylinositol 3-kinase/AKT kinase/glycogen-synthase kinase-3β (PI3K/AKT/GSK-3β) signaling pathway. Collectively, PCMT1 plays a cancer-facilitative role in PCa by promoting the proliferation, migration and invasion of PCa cells, and inhibiting apoptosis. Therefore, PCMT1 is considered to represent a novel target for treating PCa.
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Affiliation(s)
- Jiacheng Zhong
- Department of Urology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Chao Yuan
- Department of Urology, Jingzhou Central Hospital, Jingzhou 434020, China
| | - Lin Liu
- Department of Emergency, Renmin Hospital, Hubei University of Medicine, Shiyan 442000, China
| | - Yang Du
- Department of Urology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Yumin Hui
- Department of Urology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Zhiyuan Chen
- Department of Urology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Changhui Diao
- Department of Urology, The First People’s Hospital of Shangqiu City, Shangqiu 476100, China
| | - Rui Yang
- Department of Urology, Renmin Hospital of Wuhan University, Wuhan 430060, China
| | - Guiyong Liu
- Department of Urology, Qianjiang Central Hospital, Qianjiang 433100, China
| | - Xiuheng Liu
- Department of Urology, Renmin Hospital of Wuhan University, Wuhan 430060, China
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3
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Karongo R, Horak J, Lämmerhofer M. Comprehensive reversed-phase×chiral two-dimensional liquid chromatography coupled to quadrupole-time-of-flight tandem mass spectrometry with post-first dimension flow splitting for untargeted enantioselective amino acid analysis. J Sep Sci 2023; 46:e2300351. [PMID: 37464972 DOI: 10.1002/jssc.202300351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2023] [Revised: 07/04/2023] [Accepted: 07/05/2023] [Indexed: 07/20/2023]
Abstract
This work describes a comprehensive achiral × chiral two-dimensional liquid chromatography separation for enantioselective amino acid analysis coupled to electrospray ionization-tandem mass spectrometry detection using data-independent acquisition. Flow splitting after the first and second dimension separation was utilized for volumetric flow reduction and for enabling a multi-detector approach (with ultraviolet, fluorescence, charged aerosol, and MS detection), respectively. Derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate provided a chromophore, a fluorophore, and an efficient mass tag for efficient ionization in positive electrospray ionization-mass spectrometry. Chiral columns often have limitations in terms of their chemoselectivity, which may be a problem when complex sample mixtures with structurally related compounds need to be separated. It can be alleviated by a reversed-phase×chiral two-dimensional-liquid chromatography setup, in which the first dimension provides the chemoselectivity and a chiral tandem column constituted of quinine-carbamate derived weak anion-exchanger and zwitterionic ion-exchanger in the second dimension separation of D- and L-amino acid enantiomers. The method was used to control the stereointegrity of the therapeutic peptide octreotide. After hydrolysis, all amino acid constituents were detected with the correct configuration and composition. Some options for flow splitting and integration of destructive detectors in the first dimension separation are outlined.
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Affiliation(s)
- Ryan Karongo
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Tübingen, Germany
| | - Jeannie Horak
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Tübingen, Germany
- Division of Metabolic and Nutritional Medicine, Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University Munich Medical Center, Munich, Germany
| | - Michael Lämmerhofer
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Tübingen, Germany
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4
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Bashyal A, Hui JO, Flick T, Dykstra AB, Zhang Q, Campuzano IDG, Brodbelt JS. Differentiation of Aspartic and Isoaspartic Acid Using 193 nm Ultraviolet Photodissociation Mass Spectrometry. Anal Chem 2023; 95:11510-11517. [PMID: 37458293 PMCID: PMC10588209 DOI: 10.1021/acs.analchem.3c02025] [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: 08/02/2023]
Abstract
Spontaneous conversion of aspartic acid (Asp) to isoaspartic acid (isoAsp) is a ubiquitous modification that influences the structure and function of proteins. This modification of Asp impacts the stability of biotherapeutics and has been linked to the development of neurodegenerative diseases. We explored the use of 193 nm ultraviolet photodissociation (UVPD) to distinguish Asp and isoAsp in the protonated and deprotonated peptides. The differences in the relative abundances of several fragment ions uniquely generated by UVPD were used to differentiate isomeric peptide standards containing Asp or isoAsp. These fragment ions result from the cleavage of bonds N-terminal to Asp/isoAsp residues in addition to the side-chain losses from Asp/isoAsp or the losses of COOH, CO2, CO, or H2O from y-ions. Fragmentation of Asp-containing tryptic peptides using UVPD resulted in more enhanced w/w + 1/y - 1/x ions, while isoAsp-containing peptides yielded more enhanced y - 18/y - 45/y - 46 ions. UVPD was also used to identify an isomerized peptide from a tryptic digest of a monoclonal antibody. Moreover, UVPD of a protonated nontryptic peptide resulted in more enhanced y ions N- and C-terminal to isoAsp and differences in b/y ion ratios that were used to identify the isoAsp peptide.
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Affiliation(s)
- Aarti Bashyal
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - John O Hui
- Amgen Research, Molecular Analytics, Amgen Inc., Thousand Oaks, California 91320, United States
| | - Tawnya Flick
- Process Development, Attribute Sciences, Amgen Inc., Thousand Oaks, California 91320, United States
| | - Andrew B Dykstra
- Process Development, Attribute Sciences, Amgen Inc., Thousand Oaks, California 91320, United States
| | - Qingchun Zhang
- Process Development, Attribute Sciences, Amgen Inc., Thousand Oaks, California 91320, United States
| | - Iain D G Campuzano
- Amgen Research, Molecular Analytics, Amgen Inc., Thousand Oaks, California 91320, United States
| | - Jennifer S Brodbelt
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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5
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Karongo R, Horak J, Lämmerhofer M. Comprehensive Online Reversed-Phase × Chiral Two-Dimensional Liquid Chromatography-Mass Spectrometry with Data-Independent Sequential Window Acquisition of All Theoretical Fragment-Ion Spectra-Acquisition for Untargeted Enantioselective Amino Acid Analysis. Anal Chem 2022; 94:17063-17072. [PMID: 36442145 DOI: 10.1021/acs.analchem.2c03042] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This work presents an advanced analytical platform for untargeted enantioselective amino acid analysis (eAAA) by comprehensive achiral × chiral 2D-LC hyphenated to ESI-QTOF-MS/MS utilizing data-independent SWATH (sequential window acquisition of all theoretical fragment-ion spectra) technology. The methodology involves N-terminal pre-column derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC; AccQ) as retention, selectivity, and MS tag, supporting retention and UV detection in RPLC (1D), chiral recognition, and thus enantioselectivity by the core-shell tandem column composed of a quinine carbamate weak anion exchanger (QN-AX) and a zwitterionic chiral ion-exchanger (ZWIX(+)) (2D) as well as the ionization efficiency during positive electrospray ionization due to a high proton affinity of the AQC label. Furthermore, the urea-type MS tag gives rise to the generation of AQC-tag characteristic signature fragments in MS2. The latter allows the chemoselective mass spectrometric filtering of targeted and untargeted N-derivatized amino acids or related labeled species. The chiral core-shell tandem column provides a complete enantioselective amino acid profile of all proteinogenic amino acids within 1 min, with full baseline separation of all enantiomers, but without resolution of isomeric Ile/allo-Ile (aIle)/Leu, which can be resolved by RPLC. The entire LC × LC separation occurs within a total run time of 60 min (1D), with the chiral 2D operated in gradient elution mode and a cycle time of 60 s. A strategy to mine the 2D-LC-SWATH data is presented and demonstrated for the qualitative eAAA of two peptide hydrolysate samples of therapeutic peptides containing common and uncommon as well as primary and secondary amino acids. Absolute configuration assignment of amino acids using template matching for all proteinogenic amino acids was made feasible due to method robustness and the inclusion of an isotopically labeled L-[U-13C15N]-AA standard. The quantification performance of this LC × LC-MS/MS assay was also evaluated. Accuracies were acceptable for the majority of AAs enabling AA composition determination in peptide hydrolysates simultaneously with configuration assignment, as exemplified by oxytocin. This methodology represents a step toward truly untargeted 2D enantioselective amino acid analysis and metabolomics.
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Affiliation(s)
- Ryan Karongo
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany
| | - Jeannie Horak
- Division of Metabolic and Nutritional Medicine, Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University Munich Medical Center, Lindwurmstraße 4, 80337 Munich, Germany
| | - Michael Lämmerhofer
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany
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6
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Karongo R, Ge M, Geibel C, Horak J, Lämmerhofer M. Enantioselective multiple heart cutting online two-dimensional liquid chromatography-mass spectrometry of all proteinogenic amino acids with second dimension chiral separations in one-minute time scales on a chiral tandem column. Anal Chim Acta 2021; 1180:338858. [PMID: 34538327 DOI: 10.1016/j.aca.2021.338858] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 07/15/2021] [Accepted: 07/16/2021] [Indexed: 02/09/2023]
Abstract
In this work, we present a unique, robust and fully automated analytical platform technology for the enantioselective amino acid analysis using a multiple heart cutting RPLC-enantio/stereoselective HPLC-ESI-QTOF-MS method. This 2D-LC method allows the full enantioselective separation of 20 proteinogenic AAs plus 5 isobaric analogues, namely allo-Threonine (aThr), homoserine (Hse), allo-isoleucine (aIle), tert-Leucine (Tle) and Norleucine (Nle), after pre-column derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC; AccQ). This N-terminal AA-derivatization method introduces on the one hand beneficial chromatographic properties for 1D RP-LC (stronger retention) and 2D chiral separation (better chiral recognition), and on the other hand favorable detection properties with its chromophoric, fluorophoric, and easily ionizable quinoline mass tag. The entire separation occurs within a total 2DLC run time of 45 min, which includes the 1D-RP run and the 68 s 2D chiral separations of 30 heart-cuts (from the 1D-RP-run) on a chiral quinine carbamate (core-shell QNAX/fully porous ZWIX) tandem column. This relatively short overall run time was only possible by utilizing the highly efficient "smart peak parking" algorithm for the heart cuts and the resulting optimized analysis order thereof. 1D retention time precisions of <0.21% RSD were a requirement for the time-based sampling mode and finally led to a robust, fully automated enantioselective amino acid analysis platform. This achiral-chiral 2DLC method was applied for the amino acid stereoconfiguration assignment of three peptides (aureobasidin A, a lipopeptide research sample, and octreotide) using an L-[u-13C15N] labelled internal AA standard mix spiked to each sample. The isotopically labelled L-AA standard allowed an easy and straightforward identification and configuration assignment, as well as the relative quantification of amino acids within the investigated peptides, allowing the direct determination of the number of respective amino acids and their chirality within a peptide.
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Affiliation(s)
- Ryan Karongo
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Auf der Morgenstelle 8, 72076, Tübingen, Germany
| | - Min Ge
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Auf der Morgenstelle 8, 72076, Tübingen, Germany
| | - Christian Geibel
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Auf der Morgenstelle 8, 72076, Tübingen, Germany
| | - Jeannie Horak
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Auf der Morgenstelle 8, 72076, Tübingen, Germany; Division of Metabolic and Nutritional Medicine, Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University Munich Medical Center, Lindwurmstraße 4, 80337, Munich, Germany.
| | - Michael Lämmerhofer
- Institute of Pharmaceutical Sciences, Pharmaceutical (Bio-)Analysis, University of Tübingen, Auf der Morgenstelle 8, 72076, Tübingen, Germany.
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7
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Abstract
Like many biological compounds, proteins are found primarily in their homochiral form. However, homochirality is not guaranteed throughout life. Determining their chiral proteinogenic sequence is a complex analytical challenge. This is because certain d-amino acids contained in proteins play a role in human health and disease. This is the case, for example, with d-Asp in elastin, β-amyloid and α-crystallin which, respectively, have an action on arteriosclerosis, Alzheimer’s disease and cataracts. Sequence-dependent and sequence-independent are the two strategies for detecting the presence and position of d-amino acids in proteins. These methods rely on enzymatic digestion by a site-specific enzyme and acid hydrolysis in a deuterium or tritium environment to limit the natural racemization of amino acids. In this review, chromatographic and electrophoretic techniques, such as LC, SFC, GC and CE, will be recently developed (2018–2020) for the enantioseparation of amino acids and peptides. For future work, the discovery and development of new chiral stationary phases and derivatization reagents could increase the resolution of chiral separations.
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8
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Soliman R, Cordero-Maldonado ML, Martins TG, Moein M, Conrotte JF, Warmack RA, Skupin A, Crawford AD, Clarke SG, Linster CL. l-Isoaspartyl Methyltransferase Deficiency in Zebrafish Leads to Impaired Calcium Signaling in the Brain. Front Genet 2021; 11:612343. [PMID: 33552132 PMCID: PMC7859441 DOI: 10.3389/fgene.2020.612343] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 12/21/2020] [Indexed: 11/13/2022] Open
Abstract
Isomerization of l-aspartyl and l-asparaginyl residues to l-isoaspartyl residues is one type of protein damage that can occur under physiological conditions and leads to conformational changes, loss of function, and enhanced protein degradation. Protein l-isoaspartyl methyltransferase (PCMT) is a repair enzyme whose action initiates the reconversion of abnormal l-isoaspartyl residues to normal l-aspartyl residues in proteins. Many lines of evidence support a crucial role for PCMT in the brain, but the mechanisms involved remain poorly understood. Here, we investigated PCMT activity and function in zebrafish, a vertebrate model that is particularly well-suited to analyze brain function using a variety of techniques. We characterized the expression products of the zebrafish PCMT homologous genes pcmt and pcmtl. Both zebrafish proteins showed a robust l-isoaspartyl methyltransferase activity and highest mRNA transcript levels were found in brain and testes. Zebrafish morphant larvae with a knockdown in both the pcmt and pcmtl genes showed pronounced morphological abnormalities, decreased survival, and increased isoaspartyl levels. Interestingly, we identified a profound perturbation of brain calcium homeostasis in these morphants. An abnormal calcium response upon ATP stimulation was also observed in mouse hippocampal HT22 cells knocked out for Pcmt1. This work shows that zebrafish is a promising model to unravel further facets of PCMT function and demonstrates, for the first time in vivo, that PCMT plays a pivotal role in the regulation of calcium fluxes.
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Affiliation(s)
- Remon Soliman
- Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | | | - Teresa G Martins
- Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Mahsa Moein
- Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Jean-François Conrotte
- Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Rebeccah A Warmack
- Department of Chemistry and Biochemistry, The Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA, United States
| | - Alexander Skupin
- Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg.,University of California, San Diego, La Jolla, CA, United States
| | - Alexander D Crawford
- Department of Preclinical Sciences and Pathology, Norwegian University of Life Sciences, Oslo, Norway.,Institute for Orphan Drug Discovery, Bremer Innovations- und Technologiezentrum, Bremen, Germany
| | - Steven G Clarke
- Department of Chemistry and Biochemistry, The Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA, United States
| | - Carole L Linster
- Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
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9
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Fujii N, Takata T, Kim I, Matsubara T. Simultaneous and Rapid Detection of Multiple Epimers and Isomers of Aspartyl Residues in Lens Proteins Using an LC-MS-MRM Method. ACS OMEGA 2020; 5:27626-27632. [PMID: 33134726 PMCID: PMC7594319 DOI: 10.1021/acsomega.0c04197] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Accepted: 10/02/2020] [Indexed: 05/03/2023]
Abstract
Traditionally, studies of post translational modifications (PTMs) by mass analysis have been limited to modifications such as deamidation and oxidation that have a mass shift. Although Asp isomerization is an important PTM, the selective detection of Asp isomers by mass spectrometry was originally thought to be impossible due to the identical mass of the isomers. The recent development of an LC-MS-based method has facilitated rapid and accurate quantitative analysis of Asp isomers in long-lived proteins; however, because the quantification is based on the extracted ion chromatogram acquired by an MS1 scan, this methodology is not always efficient for detecting extremely low-abundance peptides in complex biological samples. In this paper, we evaluated Asp isomer-containing peptides of αA-crystallin present in tryptic digests of human lens samples with different degrees of protein aggregation and different ages using LC coupled with multiple reaction monitoring (MRM). In a single analysis, the LC-MRM method enabled three tryptic peptides containing isomers of Asp58, Asp91/92, and Asp151 to be detected simultaneously. The extent of isomerization and epimerization of these specific Asp sites in αA-crystallin increased with the progress of α-crystallin aggregation. For the analysis of samples known to isomerize at specific Asp residues, MRM gives a more rapid, less laborious, and high-quality separation of Asp isomer-containing peptides relative to the previous MS1-based quantitative method.
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Affiliation(s)
- Noriko Fujii
- Institute
for Integrated Radiation and Nuclear Science, Kyoto University, 2
Asashironishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
- . Tel.: +81-72-451-2496
| | - Takumi Takata
- Institute
for Integrated Radiation and Nuclear Science, Kyoto University, 2
Asashironishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Ingu Kim
- Institute
for Integrated Radiation and Nuclear Science, Kyoto University, 2
Asashironishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Toshiya Matsubara
- Shimadzu
Corporation, 1 Nisinokyo Kuwabara, Nakagyo-ku, Kyoto 604-8511, Japan
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10
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Mechanism of protein cleavage at asparagine leading to protein-protein cross-links. Biochem J 2020; 476:3817-3834. [PMID: 31794011 DOI: 10.1042/bcj20190743] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Revised: 12/01/2019] [Accepted: 12/03/2019] [Indexed: 12/21/2022]
Abstract
Long-lived proteins (LLPs) are present in numerous tissues within the human body. With age, they deteriorate, often leading to the formation of irreversible modifications such as peptide bond cleavage and covalent cross-linking. Currently understanding of the mechanism of formation of these cross-links is limited. As part of an ongoing study, proteomics was used to characterise sites of novel covalent cross-linking in the human lens. In this process, Lys residues were found cross-linked to C-terminal aspartates that had been present in the original protein as Asn residues. Cross-links were identified in major lens proteins such as αA-crystallin, αB-crystallin and aquaporin 0. Quantification of the level of an AQP0/AQP0 cross-linked peptide showed increased cross-linking with age and in cataract lenses. Using model peptides, a mechanism of cross-link formation was elucidated that involves spontaneous peptide bond cleavage on the C-terminal side of Asn residues resulting in the formation of a C-terminal succinimide. This succinimide does not form cross-links, but can hydrolyse to a mixture of C-terminal Asn and C-terminal Asp amide peptides. The C-terminal Asp amide is unstable at neutral pH and decomposes to a succinic anhydride. If the side chain of Lys attacks the anhydride, a covalent cross-link will be formed. This multi-step mechanism represents a link between two spontaneous events: peptide bond cleavage at Asn and covalent cross-linking. Since Asn deamidation and cleavage are abundant age-related modifications in LLPs, this finding suggests that such susceptible Asn residues should also be considered as potential sites for spontaneous covalent cross-linking.
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11
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Fujii N, Takata T, Kim I, Morishima K, Inoue R, Magami K, Matsubara T, Sugiyama M, Koide T. Asp isomerization increases aggregation of α-crystallin and decreases its chaperone activity in human lens of various ages. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2020; 1868:140446. [PMID: 32442520 DOI: 10.1016/j.bbapap.2020.140446] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 05/12/2020] [Accepted: 05/14/2020] [Indexed: 10/24/2022]
Abstract
α-Crystallin, comprising 40-50 subunits of αA- and αB-subunits, is a long-lived major soluble chaperone protein in lens. During aging, α-crystallin forms aggregates of high molecular weight (HMW) protein and eventually becomes water-insoluble (WI). Isomerization of Asp in α-crystallin has been proposed as a trigger of protein aggregation, ultimately leading to cataract formation. Here, we have investigated the relationship between protein aggregation and Asp isomerization of αA-crystallin by a series of analyses of the soluble α-crystallin, HMW and WI fractions from human lens samples of different ages (10-76 years). Analytical ultracentrifugation showed that the HMW fraction had a peak sedimentation coefficient of 40 S and a wide distribution of values (10-450 S) for lens of all ages, whereas the α-crystallin had a much smaller peak sedimentation coefficient (10-20 S) and was less heterogeneous, regardless of lens age. Measurement of the ratio of isomers (Lα-, Lβ-, Dα-, Dβ-) at Asp58, Asp91/92 and Asp151 in αA-crystallin by liquid chromatography-mass spectrometry showed that the proportion of isomers at all three sites increased in order of aggregation level (α-crystallin < HMW < WI fractions). Among the abnormal isomers of Asp58 and Asp151, Dβ-isomers were predominant with a very few exceptions. Notably, the chaperone activity of HMW protein was minimal for lens of all ages, whereas that of α-crystallin decreased with increasing lens age. Thus, abnormal aggregation caused by Asp isomerization might contribute to the loss of chaperone activity of α-crystallin in aged human lens.
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Affiliation(s)
- Noriko Fujii
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan.
| | - Takumi Takata
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Ingu Kim
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Ken Morishima
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Rintaro Inoue
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Kousuke Magami
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | | | - Masaaki Sugiyama
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Tamaki Koide
- Rexxam Co., Ltd., Nishi-ku, Nagoya, Aichi 541-0054, Japan
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12
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Magami K, Kim I, Fujii N. A single Asp isomer substitution in an αA-crystallin-derived peptide induces a large change in peptide properties. Exp Eye Res 2020; 192:107930. [DOI: 10.1016/j.exer.2020.107930] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 01/07/2020] [Accepted: 01/08/2020] [Indexed: 10/25/2022]
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13
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Truscott RJW, Friedrich MG. Molecular Processes Implicated in Human Age-Related Nuclear Cataract. Invest Ophthalmol Vis Sci 2020; 60:5007-5021. [PMID: 31791064 PMCID: PMC7043214 DOI: 10.1167/iovs.19-27535] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Human age-related nuclear cataract is commonly characterized by four biochemical features that involve modifications to the structural proteins that constitute the bulk of the lens: coloration, oxidation, insolubility, and covalent cross-linking. Each of these is progressive and increases as the cataract worsens. Significant progress has been made in understanding the origin of the factors that underpin the loss of lens transparency. Of these four hallmarks of cataract, it is protein-protein cross-linking that has been the most intransigent, and it is only recently, with the advent of proteomic methodology, that mechanisms are being elucidated. A diverse range of cross-linking processes involving several amino acids have been uncovered. Although other hypotheses for the etiology of cataract have been advanced, it is likely that spontaneous decomposition of the structural proteins of the lens, which do not turn over, is responsible for the age-related changes to the properties of the lens and, ultimately, for cataract. Cataract may represent the first and best characterized of a number of human age-related diseases where spontaneous protein modification leads to ongoing deterioration and, ultimately, a loss of tissue function.
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Affiliation(s)
- Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
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14
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Schey KL, Wang Z, Friedrich MG, Garland DL, Truscott RJW. Spatiotemporal changes in the human lens proteome: Critical insights into long-lived proteins. Prog Retin Eye Res 2019; 76:100802. [PMID: 31704338 DOI: 10.1016/j.preteyeres.2019.100802] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 10/24/2019] [Accepted: 10/30/2019] [Indexed: 12/15/2022]
Abstract
The ocular lens is a unique tissue that contains an age gradient of cells and proteins ranging from newly differentiated cells containing newly synthesized proteins to cells and proteins that are as old as the organism. Thus, the ocular lens is an excellent model for studying long-lived proteins (LLPs) and the effects of aging and post-translational modifications on protein structure and function. Given the architecture of the lens, with young fiber cells in the outer cortex and the oldest cells in the lens nucleus, spatially-resolved studies provide information on age-specific protein changes. In this review, experimental strategies and proteomic methods that have been used to examine age-related and cataract-specific changes to the human lens proteome are described. Measured spatio-temporal changes in the human lens proteome are summarized and reveal a highly consistent, time-dependent set of modifications observed in transparent human lenses. Such measurements have led to the discovery of cataract-specific modifications and the realization that many animal systems are unsuitable to study many of these modifications. Mechanisms of protein modifications such as deamidation, racemization, truncation, and protein-protein crosslinking are presented and the implications of such mechanisms for other long-lived proteins in other tissues are discussed in the context of age-related neurological diseases. A comprehensive understanding of LLP modifications will enhance our ability to develop new therapies for the delay, prevention or reversal of age-related diseases.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry, Vanderbilt University, USA.
| | - Zhen Wang
- Department of Biochemistry, Vanderbilt University, USA
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
| | | | - Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
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15
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Riggs DL, Silzel JW, Lyon YA, Kang AS, Julian RR. Analysis of Glutamine Deamidation: Products, Pathways, and Kinetics. Anal Chem 2019; 91:13032-13038. [PMID: 31498611 PMCID: PMC8805438 DOI: 10.1021/acs.analchem.9b03127] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Spontaneous chemical modifications play an important role in human disease and aging at the molecular level. Deamidation and isomerization are known to be among the most prevalent chemical modifications in long-lived human proteins and are implicated in a growing list of human pathologies, but the relatively minor chemical change associated with these processes has presented a long standing analytical challenge. Although the adoption of high-resolution mass spectrometry has greatly aided the identification of deamidation sites in proteomic studies, isomerization (and the isomeric products of deamidation) remain exceptionally challenging to characterize. Herein, we present a liquid chromatography/mass spectrometry-based approach for rapidly characterizing the isomeric products of Gln deamidation using diagnostic fragments that are abundantly produced and capable of unambiguously identifying both Glu and isoGlu. Importantly, the informative fragment ions are produced through orthogonal fragmentation pathways, thereby enabling the simultaneous detection of both isomeric forms while retaining compatibility with shotgun proteomics. Furthermore, the diagnostic fragments associated with isoGlu pinpoint the location of the modified residue. The utility of this technique is demonstrated by characterizing the isomeric products generated during in vitro aging of a series of glutamine-containing peptides. Sequence-dependent product profiles are obtained, and the abundance of deamidation-linked racemization is examined. Finally, comparisons are made between Gln deamidation, which is relatively poorly understood, and asparagine deamidation, which has been more thoroughly studied.
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Affiliation(s)
- Dylan L. Riggs
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Jacob W. Silzel
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Yana A. Lyon
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Amrik S. Kang
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Ryan R. Julian
- Department of Chemistry, University of California, Riverside, California 92521, United States
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16
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López-Valencia D, Medina-Ortega Á, Hoyos-Samboní DF, Saavedra-Torres JS, Salguero C. Epstein-Barr virus infection as a predisposing factor for multiple sclerosis. An update from molecular biology, immunology and epidemiology. REVISTA DE LA FACULTAD DE MEDICINA 2019. [DOI: 10.15446/revfacmed.v67n3.70149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Introduction: Epstein-Barr virus is an infectious agent used to immortalize and induce polyclonal activation of B cells. It has been widely described that this virus produces changes in the cells it infects and in the immune response, and stimulates the development of autoimmune diseases.Objective: To characterize the association between Epstein-Barr virus and multiple sclerosis described in current scientific literature.Materials and methods: A 59-years range literature search was conducted in the PubMed, ScienceDirect, Redalyc and SciELO databases using the following MeSH terms: “Epstein-Barr virus, multiple sclerosis autoimmune diseases, autoimmune diseases of the nervous system”.Results: Many studies describe the association between Epstein-Barr virus and multiple sclerosis. It is believed that acute infection and viral reactivation promote the development of multiple sclerosis.Conclusions: It is necessary to conduct further research on the pathogenesis and morphophysiological and neuroimmunological changes –at the ecological, molecular, cellular, tissue, organic and systemic level– induced by the immune response and that favor the development of multiple sclerosis.
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17
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Wang Z, Friedrich MG, Truscott RJW, Schey KL. Cleavage C-terminal to Asp leads to covalent crosslinking of long-lived human proteins. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1867:831-839. [PMID: 31226490 DOI: 10.1016/j.bbapap.2019.06.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Revised: 05/29/2019] [Accepted: 06/16/2019] [Indexed: 01/27/2023]
Abstract
With age, long-lived proteins in the human body deteriorate, which can have consequences both for aging and disease. The aging process is often associated with the formation of covalently crosslinked proteins. Currently our knowledge of the mechanism of formation of these crosslinks is limited. In this study, proteomics was used to characterize sites of covalent protein-protein crosslinking and identify a novel mechanism of protein-protein crosslinking in the adult human lens. In this mechanism, Lys residues are crosslinked to C-terminal Asp residues that are formed by non-enzymatic protein truncation. Ten different crosslinks were identified in major lens proteins such as αA-crystallin, αB-crystallin and AQP0. Crosslinking in AQP0 increased significantly with age and also increased significantly in cataract lenses compared with normal lenses. Using model peptides, a mechanism of formation of the Lys-Asp crosslink was elucidated. The mechanism involves spontaneous peptide cleavage on the C-terminal side of Asp residues which can take place in the pH range 5-7.4. Cleavage appears to involve attack by the side chain carboxyl group on the adjacent peptide bond, resulting in the formation of a C-terminal Asp anhydride. This anhydride intermediate can then either react with water to form Asp, or with a nucleophile, such as a free amine group to form a crosslink. If an ε-amino group of Lys or an N-terminal amine group attacks the anhydride, a covalent protein-protein crosslink will be formed. This bi-phasic mechanism represents the first report to link two spontaneous events: protein cleavage and crosslinking that are characteristic of long-lived proteins.
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Affiliation(s)
- Zhen Wang
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW 2522, Australia
| | - Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW 2522, Australia.
| | - Kevin L Schey
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, TN, USA.
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18
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Faigle W, Cruciani C, Wolski W, Roschitzki B, Puthenparampil M, Tomas-Ojer P, Sellés-Moreno C, Zeis T, Jelcic I, Schaeren-Wiemers N, Sospedra M, Martin R. Brain Citrullination Patterns and T Cell Reactivity of Cerebrospinal Fluid-Derived CD4 + T Cells in Multiple Sclerosis. Front Immunol 2019; 10:540. [PMID: 31024521 PMCID: PMC6467957 DOI: 10.3389/fimmu.2019.00540] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Accepted: 02/27/2019] [Indexed: 01/11/2023] Open
Abstract
Immune responses to citrullinated peptides have been described in autoimmune diseases like rheumatoid arthritis (RA) and multiple sclerosis (MS). We investigated the post-translational modification (PTM), arginine to citrulline, in brain tissue of MS patients and controls (C) by proteomics and subsequently the cellular immune response of cerebrospinal fluid (CSF)-infiltrating T cells to citrullinated and unmodified peptides of myelin basic protein (MBP). Using specifically adapted tissue extraction- and combined data interpretation protocols we could establish a map of citrullinated proteins by identifying more than 80 proteins with two or more citrullinated peptides in human brain tissue. We report many of them for the first time. For the already described citrullinated proteins MBP, GFAP, and vimentin, we could identify additional citrullinated sites. The number of modified proteins in MS white matter was higher than control tissue. Citrullinated peptides are considered neoepitopes that may trigger autoreactivity. We used newly identified epitopes and previously reported immunodominant myelin peptides in their citrullinated and non-citrullinated form to address the recognition of CSF-infiltrating CD4+ T cells from 22 MS patients by measuring proliferation and IFN-γ secretion. We did not detect marked responses to citrullinated peptides, but slightly more strongly to the non-modified version. Based on these data, we conclude that citrullination does not appear to be an important activating factor of a T cell response, but could be the consequence of an immune- or inflammatory response. Our approach allowed us to perform a deep proteome analysis and opens new technical possibilities to analyze complex PTM patterns on minute quantities of rare tissue samples.
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Affiliation(s)
- Wolfgang Faigle
- Neuroimmunology and MS Research Section, Neurology Clinic, University Zurich, University Hospital Zurich, Zurich, Switzerland
| | - Carolina Cruciani
- Neuroimmunology and MS Research Section, Neurology Clinic, University Zurich, University Hospital Zurich, Zurich, Switzerland
| | - Witold Wolski
- Functional Genomics Center Zurich, ETH Zurich & University of Zurich, Zurich, Switzerland
| | - Bernd Roschitzki
- Functional Genomics Center Zurich, ETH Zurich & University of Zurich, Zurich, Switzerland
| | - Marco Puthenparampil
- Neuroimmunology and MS Research Section, Neurology Clinic, University Zurich, University Hospital Zurich, Zurich, Switzerland
| | - Paula Tomas-Ojer
- Neuroimmunology and MS Research Section, Neurology Clinic, University Zurich, University Hospital Zurich, Zurich, Switzerland
| | - Carla Sellés-Moreno
- Neuroimmunology and MS Research Section, Neurology Clinic, University Zurich, University Hospital Zurich, Zurich, Switzerland
| | - Thomas Zeis
- Neurobiology, Department of Biomedicine, University Hospital Basel, University of Basel, Basel, Switzerland
| | - Ivan Jelcic
- Neuroimmunology and MS Research Section, Neurology Clinic, University Zurich, University Hospital Zurich, Zurich, Switzerland
| | - Nicole Schaeren-Wiemers
- Neurobiology, Department of Biomedicine, University Hospital Basel, University of Basel, Basel, Switzerland
| | - Mireia Sospedra
- Neuroimmunology and MS Research Section, Neurology Clinic, University Zurich, University Hospital Zurich, Zurich, Switzerland
| | - Roland Martin
- Neuroimmunology and MS Research Section, Neurology Clinic, University Zurich, University Hospital Zurich, Zurich, Switzerland
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19
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Fujii N, Takata T, Fujii N, Aki K, Sakaue H. D-Amino acids in protein: The mirror of life as a molecular index of aging. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2018. [DOI: 10.1016/j.bbapap.2018.03.001] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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20
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Riggs DL, Gomez SV, Julian RR. Sequence and Solution Effects on the Prevalence of d-Isomers Produced by Deamidation. ACS Chem Biol 2017; 12:2875-2882. [PMID: 28984444 PMCID: PMC5696650 DOI: 10.1021/acschembio.7b00686] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Deamidation of asparagine is a spontaneous and irreversible post-translational modification associated with a growing list of human diseases. While pervasive, deamidation is often overlooked because it represents a relatively minor chemical change. Structural and functional characterization of this modification is complicated because deamidation of asparagine yields four isomeric forms of Asp. Herein, radical directed dissociation (RDD), in conjunction with mass spectrometry, is used to identify and quantify all four isomers in a series of model peptides that were subjected to various deamidation conditions. Although primary sequence significantly influences the rate of deamidation, it has little impact on the relative proportions of the product isomers. Furthermore, the addition of ammonia can be used to increase the rate of deamidation without significantly perturbing isomer populations. Conversely, external factors such as buffer conditions and temperature alter product distributions but exhibit less dramatic effects on the deamidation rate. Strikingly, the common laboratory and biologically significant bicarbonate buffer is found to strongly promote racemization, yielding increased amounts of d-Asp and d-isoAsp. These outcomes following deamidation have broad implications in human aging and should be considered during the development of protein-based therapeutics.
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Affiliation(s)
- Dylan L. Riggs
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Sonia V. Gomez
- Department of Chemistry, University of California, Riverside, California 92521, United States
| | - Ryan R. Julian
- Department of Chemistry, University of California, Riverside, California 92521, United States
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21
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Sarg B, Faserl K, Lindner HH. Identification of Novel Site-Specific Alterations in the Modification Level of Myelin Basic Protein Isolated from Mouse Brain at Different Ages Using Capillary Electrophoresis-Mass Spectrometry. Proteomics 2017; 17. [DOI: 10.1002/pmic.201700269] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 07/07/2017] [Indexed: 12/20/2022]
Affiliation(s)
- Bettina Sarg
- Division of Clinical Biochemistry, Biocenter; Medical University of Innsbruck; Innsbruck Austria
| | - Klaus Faserl
- Division of Clinical Biochemistry, Biocenter; Medical University of Innsbruck; Innsbruck Austria
| | - Herbert H. Lindner
- Division of Clinical Biochemistry, Biocenter; Medical University of Innsbruck; Innsbruck Austria
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22
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Harauz G. And Yet it is Modified-Holding a Candle to the Dark Matter of White Matter. Proteomics 2017; 17. [PMID: 28851044 DOI: 10.1002/pmic.201700299] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Indexed: 11/08/2022]
Abstract
The multilamellar membrane myelin sheath of the CNS, that enwraps axons to facilitate saltatory conduction in higher vertebrates, is held together by myelin basic protein (MBP). Yet this generalization masks how enigmatic MBP is, much like cosmological "dark matter." First, the casual use of the singular form for "protein" distracts that there are multiple, developmentally regulated "classic" splice isoforms ranging from 14 to 21.5 kDa, each with extensive PTMs. Second, the static image of MBP adhering two cytoplasmic leaflets of the oligodendrocyte membrane together in close apposition, suggests it to be inaccessible to modifying enzymes. And yet it is modified (to paraphrase Galileo's phrase on the earth's motion). In this issue of Proteomics, Sarg et al. apply an integrated CE-MS approach to investigate the PTMs of 18.5 kDa MBP from mouse brains of different ages. They identify new sites and types of modification, as well as confirming previously known PTMs. Innovative tools for unraveling the intricacies of the myelin basic proteome and how it organizes CNS myelin (much like basic histones organize chromatin), will help us understand white matter development and plasticity in health, during ageing, and in demyelinating diseases such as multiple sclerosis.
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Affiliation(s)
- George Harauz
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Canada
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