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Kouloulia S, Hallin EI, Simbriger K, Amorim IS, Lach G, Amvrosiadis T, Chalkiadaki K, Kampaite A, Truong VT, Hooshmandi M, Jafarnejad SM, Skehel P, Kursula P, Khoutorsky A, Gkogkas CG. Raptor-Mediated Proteasomal Degradation of Deamidated 4E-BP2 Regulates Postnatal Neuronal Translation and NF-κB Activity. Cell Rep 2020; 29:3620-3635.e7. [PMID: 31825840 PMCID: PMC6915327 DOI: 10.1016/j.celrep.2019.11.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2019] [Revised: 09/06/2019] [Accepted: 11/06/2019] [Indexed: 12/14/2022] Open
Abstract
The translation initiation repressor 4E-BP2 is deamidated in the brain on asparagines N99/N102 during early postnatal brain development. This post-translational modification enhances 4E-BP2 association with Raptor, a central component of mTORC1 and alters the kinetics of excitatory synaptic transmission. We show that 4E-BP2 deamidation is neuron specific, occurs in the human brain, and changes 4E-BP2 subcellular localization, but not its disordered structure state. We demonstrate that deamidated 4E-BP2 is ubiquitinated more and degrades faster than the unmodified protein. We find that enhanced deamidated 4E-BP2 degradation is dependent on Raptor binding, concomitant with increased association with a Raptor-CUL4B E3 ubiquitin ligase complex. Deamidated 4E-BP2 stability is promoted by inhibiting mTORC1 or glutamate receptors. We further demonstrate that deamidated 4E-BP2 regulates the translation of a distinct pool of mRNAs linked to cerebral development, mitochondria, and NF-κB activity, and thus may be crucial for postnatal brain development in neurodevelopmental disorders, such as ASD. Deamidated 4E-BP2 occurs in neurons and is susceptible to ubiquitination/degradation mTORC1 or glutamate receptor inhibition stabilizes deamidated 4E-BP2 A Raptor-CUL4B ubiquitin ligase complex binds to deamidated 4E-BP2 Deamidated 4E-BP2 regulates postnatal brain translation and NF-κB activity
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Affiliation(s)
- Stella Kouloulia
- Centre for Discovery Brain Sciences and Patrick Wild Centre, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Erik I Hallin
- Department of Biomedicine, University of Bergen, Bergen N-5020, Norway
| | - Konstanze Simbriger
- Centre for Discovery Brain Sciences and Patrick Wild Centre, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Inês S Amorim
- Centre for Discovery Brain Sciences and Patrick Wild Centre, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Gilliard Lach
- Centre for Discovery Brain Sciences and Patrick Wild Centre, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Theoklitos Amvrosiadis
- Centre for Discovery Brain Sciences and Patrick Wild Centre, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Kleanthi Chalkiadaki
- Centre for Discovery Brain Sciences and Patrick Wild Centre, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Agniete Kampaite
- Centre for Discovery Brain Sciences and Patrick Wild Centre, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Vinh Tai Truong
- Department of Anesthesia and Alan Edwards Centre for Research on Pain, McGill University, Montréal H3A 0G1, QC, Canada
| | - Mehdi Hooshmandi
- Department of Anesthesia and Alan Edwards Centre for Research on Pain, McGill University, Montréal H3A 0G1, QC, Canada
| | - Seyed Mehdi Jafarnejad
- Centre for Cancer Research and Cell Biology, Queen's University of Belfast, Belfast BT9 7AE, UK
| | - Paul Skehel
- Centre for Discovery Brain Sciences and Patrick Wild Centre, University of Edinburgh, Edinburgh EH8 9XD, UK
| | - Petri Kursula
- Department of Biomedicine, University of Bergen, Bergen N-5020, Norway; Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu FI-90014, Finland
| | - Arkady Khoutorsky
- Department of Anesthesia and Alan Edwards Centre for Research on Pain, McGill University, Montréal H3A 0G1, QC, Canada.
| | - Christos G Gkogkas
- Centre for Discovery Brain Sciences and Patrick Wild Centre, University of Edinburgh, Edinburgh EH8 9XD, UK; Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh EH8 9XD, UK.
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Jia G, Yang H, Diao Z, Liu Y, Sun C. Neural stem cell conditioned medium alleviates Aβ 25-35 damage to SH-SY5Y cells through the PCMT1/MST1 pathway. Eur J Histochem 2020; 64:3135. [PMID: 32705859 PMCID: PMC7388643 DOI: 10.4081/ejh.2020.3135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2020] [Accepted: 05/29/2020] [Indexed: 11/27/2022] Open
Abstract
Alzheimer's disease (AD) is a progressive, neurodegenerative disease. Accumulating evidence suggests that protein isoaspartate methyltransferase 1 (PCMT1) is highly expressed in brain tissue (substantia nigra, blue plaque, paraventricular nucleus). In this study, we investigated the effect of neural stem cell conditioned medium alleviates Aβ25-35 damage to SH-SY5Y cells by PCMT1/MST1 pathway. Results demonstrated that Aβ25-35 significantly decreased the cell viability in time and dose dependent manner. However, Neural stem cell-complete medium (NSC-CPM) or NSC-CDM had inhibitory effect on toxicity when fibrillation of Aβ25-35 occurred in their presence and NSC-CDM had a better inhibitor result. An increase of the PCMT1 expression levels was found in Aβ25-35 + NSC-CDM group. sh-PCMT1 significantly reduced the PCMT1, the cell viability and inhibited the protective effect; induced apoptosis and increased the expression of p-MST1. Overexpression of PCMT1 group reversed the effect of Aβ25-35 inhibited the cell viability and Aβ25-35 induced the apoptosis. In conclusion, NSC-CDM corrects the damage of Aβ25-35 to cells by increasing PCMT1, reducing MST phosphorylation.
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Affiliation(s)
- Guoyong Jia
- Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan.
| | - Hongna Yang
- Department of Critical-care Medicine, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan.
| | - Zengyan Diao
- Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan.
| | - Ying Liu
- Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan.
| | - Congcong Sun
- Department of Neurology, Qilu Hospital, Cheeloo College of Medicine, Shandong University, Jinan.
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Cao M, Xu W, Niu B, Kabundi I, Luo H, Prophet M, Chen W, Liu D, Saveliev SV, Urh M, Wang J. An Automated and Qualified Platform Method for Site-Specific Succinimide and Deamidation Quantitation Using Low-pH Peptide Mapping. J Pharm Sci 2019; 108:3540-3549. [DOI: 10.1016/j.xphs.2019.07.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Revised: 07/26/2019] [Accepted: 07/26/2019] [Indexed: 10/26/2022]
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Mishra PKK, Mahawar M. PIMT-Mediated Protein Repair: Mechanism and Implications. BIOCHEMISTRY (MOSCOW) 2019; 84:453-463. [PMID: 31234761 DOI: 10.1134/s0006297919050018] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Amino acids undergo many covalent modifications, but only few amino acid repair enzymes have been identified. Protein-L-isoaspartate (D-aspartate) O-methyltransferase (PIMT), also known as L-isoaspartyl/D-aspartyl protein carboxyl methyltransferase (PCMT), methylates covalently modified isoaspartate (isoAsp) residues accumulated in proteins via Asn deamidation and Asp hydrolysis. This cytoplasmic reaction occurs through the formation of succinimide cyclical intermediate and generates either isoAsp or Asp from succinimide. Succinimide conversion into Asp is spontaneous, while isoAsp is restored by PIMT using S-adenosylmethionine as a methyl donor. PIMT transforms isoAsp into succinimide, thereby creating an opportunity for the later to be converted into Asp. Apart from normal cell physiology, formation of isoAsp in proteins is promoted by various stress conditions. The resulting isoAsp can form a kink or bend in the protein backbone thus making the protein conformationally and functionally distorted. Many PIMT-interacting proteins (proteins with isoAsp residues) have been reported in eukaryotes, but only few of them have been found in prokaryotes. Extensive studies in mice have shown the importance of PIMT in neurodegeneration. Detail elucidation of PIMT function can create a platform for addressing various disorders such as Alzheimer's disease and cancer.
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Affiliation(s)
- P K K Mishra
- Division of Biochemistry, Indian Veterinary Research Institute, Izatnagar, Bareilly, Uttar Pradesh, 243122, India.
| | - M Mahawar
- Division of Biochemistry, Indian Veterinary Research Institute, Izatnagar, Bareilly, Uttar Pradesh, 243122, India.
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Nakayoshi T, Kato K, Fukuyoshi S, Takahashi O, Kurimoto E, Oda A. Comparison of the activation energy barrier for succinimide formation from α- and β-aspartic acid residues obtained from density functional theory calculations. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2018; 1866:759-766. [PMID: 29305913 DOI: 10.1016/j.bbapap.2017.12.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2017] [Revised: 12/22/2017] [Accepted: 12/28/2017] [Indexed: 10/18/2022]
Abstract
The l-α-Asp residues in peptides or proteins are prone to undergo nonenzymatic reactions to form l-β-Asp, d-α-Asp, and d-β-Asp residues via a succinimide five-membered ring intermediate. From these three types of isomerized aspartic acid residues, particularly d-β-Asp has been widely detected in aging tissue. In this study, we computationally investigated the cyclization of α- and β-Asp residues to form succinimide with dihydrogen phosphate ion as a catalyst (H2PO4-). We performed the study using B3LYP/6-31+G(d,p) density functional theory calculations. The comparison of the activation barriers of both residues is discussed. All the calculations were performed using model compounds in which an α/β-Asp-Gly sequence is capped with acetyl and methylamino groups on the N- and C-termini, respectively. Moreover, H2PO4- catalyzes all the steps of the succinimide formation (cyclization-dehydration) acting as a proton-relay mediator. The calculated activation energy barriers for succinimide formation of α- and β-Asp residues are 26.9 and 26.0kcalmol-1, respectively. Although it was experimentally confirmed that β-Asp has higher stability than α-Asp, there was no clear difference between the activation barriers. Therefore, the higher stability of β-Asp residue than α-Asp residue may be caused by an entropic effect associated with the succinimide formation.
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Affiliation(s)
- Tomoki Nakayoshi
- Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa 920-1192, Japan; Faculty of Pharmacy, Meijo University, Nagoya 468-0077, Japan
| | - Koichi Kato
- Faculty of Pharmacy, Meijo University, Nagoya 468-0077, Japan; Department of Pharmacy, Kinjo Gakuin University, 463-8521 Nagoya, Japan
| | - Shuichi Fukuyoshi
- Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa 920-1192, Japan
| | - Ohgi Takahashi
- Faculty of Pharmaceutical Sciences, Tohoku Medical and Pharmaceutical University, Sendai 981-8558, Japan
| | - Eiji Kurimoto
- Faculty of Pharmacy, Meijo University, Nagoya 468-0077, Japan
| | - Akifumi Oda
- Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa 920-1192, Japan; Faculty of Pharmacy, Meijo University, Nagoya 468-0077, Japan; Institute for Protein Research, Osaka University, Suita 565-0871, Japan.
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6
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Eukaryotic initiation factor 4E-binding protein 1 (4E-BP1): a master regulator of mRNA translation involved in tumorigenesis. Oncogene 2016; 35:4675-88. [DOI: 10.1038/onc.2015.515] [Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 12/11/2015] [Accepted: 12/11/2015] [Indexed: 01/17/2023]
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Qin Z, Dimitrijevic A, Aswad DW. Accelerated protein damage in brains of PIMT+/- mice; a possible model for the variability of cognitive decline in human aging. Neurobiol Aging 2014; 36:1029-36. [PMID: 25465735 DOI: 10.1016/j.neurobiolaging.2014.10.036] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2014] [Revised: 10/14/2014] [Accepted: 10/27/2014] [Indexed: 12/18/2022]
Abstract
Isoaspartate formation is a common type of protein damage normally kept in check by the repair enzyme protein-L-isoaspartyl methyltransferase (PIMT). Mice with a knockout of the gene (Pcmt1) for this enzyme (KO, -/-) exhibit a pronounced neuropathology with fatal epileptic seizures at 30-60 days. Heterozygous (HZ, +/-) mice have 50% of the PIMT activity found in wild-type (WT, +/+) mice, but appear normal. To see if HZ mice exhibit accelerated aging at the molecular level, we compared brain extracts from HZ and WT mice at 8 months and 2 years with regard to PIMT activity, isoaspartate levels, and activity of an endogenous PIMT substrate, creatine kinase B. PIMT activity declined modestly with age in both genotypes. Isoaspartate was significantly higher in HZ than WT mice at 8 months and more so at 2 years, rising 5× faster in HZ males and 3× faster in females. Creatine kinase activity decreased with age and was always lower in the HZ mice. These findings suggest the individual variation of human PIMT levels may significantly influence the course of age-related central nervous system dysfunction.
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Affiliation(s)
- Zhenxia Qin
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, USA
| | - Aleksandra Dimitrijevic
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, USA
| | - Dana W Aswad
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, USA.
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Fonseca BD, Smith EM, Yelle N, Alain T, Bushell M, Pause A. The ever-evolving role of mTOR in translation. Semin Cell Dev Biol 2014; 36:102-12. [PMID: 25263010 DOI: 10.1016/j.semcdb.2014.09.014] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Revised: 09/12/2014] [Accepted: 09/15/2014] [Indexed: 02/06/2023]
Abstract
Control of translation allows for the production of stoichiometric levels of each protein in the cell. Attaining such a level of fine-tuned regulation of protein production requires the coordinated temporal and spatial control of numerous cellular signalling cascades impinging on the various components of the translational machinery. Foremost among these is the mTOR signalling pathway. The mTOR pathway regulates both the initiation and elongation steps of protein synthesis through the phosphorylation of numerous translation factors, while simultaneously ensuring adequate folding of nascent polypeptides through co-translational degradation of misfolded proteins. Perhaps most remarkably, mTOR is also a key regulator of the synthesis of ribosomal proteins and translation factors themselves. Two seminal studies have recently shown in translatome analysis that the mTOR pathway preferentially regulates the translation of mRNAs encoding ribosomal proteins and translation factors. Therefore, the role of the mTOR pathway in the control of protein synthesis extends far beyond immediate translational control. By controlling ribosome production (and ultimately ribosome availability), mTOR is a master long-term controller of protein synthesis. Herein, we review the literature spanning the early discoveries of mTOR on translation to the latest advances in our understanding of how the mTOR pathway controls the synthesis of ribosomal proteins.
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Affiliation(s)
- Bruno D Fonseca
- Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada.
| | - Ewan M Smith
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Nicolas Yelle
- Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada
| | - Tommy Alain
- Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada
| | - Martin Bushell
- MRC Toxicology Unit, Hodgkin Building, Lancaster Road, Leicester LE1 9HN, UK
| | - Arnim Pause
- Goodman Cancer Research Centre, Department of Biochemistry, McGill University, Montreal, QC H3A 1A3, Canada.
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Qin Z, Yang J, Klassen HJ, Aswad DW. Isoaspartyl protein damage and repair in mouse retina. Invest Ophthalmol Vis Sci 2014; 55:1572-9. [PMID: 24550364 DOI: 10.1167/iovs.13-13668] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
PURPOSE To determine the propensity of retinal proteins for spontaneous damage via formation of isoaspartyl sites, a common type of protein damage that could contribute to retinal disease. METHODS Tissue extracts were obtained from retinas and brains of control mice and from mice in which the gene for protein L-isoaspartate O-methyltransferase (PIMT; an enzyme that repairs isoaspartyl protein damage) was knocked out. PIMT expression in these extracts was measured by Western blot, and its specific activity was assayed by monitoring the rate of [(3)H]methyl transfer from S-adenosyl-[methyl-(3)H]L-methionine to γ-globulin. Isoaspartate levels in extracts were measured by their capacity to accept [(3)H]methyl groups via the PIMT-catalyzed methylation reaction. To compare molecular weight distributions of isoaspartyl-rich proteins in retina versus brain, proteins from PIMT knockout (KO) and control mice were separated by SDS-PAGE and transferred to polyvinylidene difluoride (PVDF). Isoaspartyl proteins were (3)H-labeled on-blot using a PIMT overlay and imaged by autoradiography. RESULTS When normalized to the β-actin content of each tissue, retina was found to be nearly identical to brain with regard to expression and activity of PIMT and its propensity to accumulate isoaspartyl sites when PIMT is absent. The two tissues show distinct differences in the molecular weight distribution of isoaspartyl proteins. CONCLUSIONS The retina is rich in PIMT activity and contains a wide range of proteins that are highly susceptible to this type of protein damage. Recoverin may be one such protein. Isoaspartate formation, along with oxidation, should be considered as a potential source of protein dysfunction and autoimmunity in retinal disease.
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Affiliation(s)
- Zhenxia Qin
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California
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Qin Z, Kaufman RS, Khoury RN, Khoury MK, Aswad DW. Isoaspartate accumulation in mouse brain is associated with altered patterns of protein phosphorylation and acetylation, some of which are highly sex-dependent. PLoS One 2013; 8:e80758. [PMID: 24224061 PMCID: PMC3818261 DOI: 10.1371/journal.pone.0080758] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Accepted: 10/14/2013] [Indexed: 12/05/2022] Open
Abstract
Isoaspartate (isoAsp) formation is a major source of protein damage that is kept in check by the repair function of protein L-isoaspartyl methyltransferase (PIMT). Mice deficient in PIMT accumulate isoAsp-containing proteins, resulting in cognitive deficits, abnormal neuronal physiology and cytoarchitecture, and fatal epileptic seizures 30–60 days after birth. Synapsins I and II, dynamin-1, collapsin response mediator protein 2 (CRMP2), and α/β-tubulin are major targets of PIMT in brain. To investigate links between isoAsp accumulation and the neurological phenotype of the KO mice, we used Western blotting to compare patterns of in vivo phosphorylation or acetylation of the major PIMT targets listed above. Phosphorylations of synapsins I and II at Ser-9 were increased in female KO vs. WT mice, and acetylation of tubulin at Lys-40 was decreased in male KO vs. WT mice. Average levels of dynamin-1 phosphorylation at Ser-778 and Ser-795 were higher in male KO vs. WT mice, but the statistical significance (P>0.1) was low. No changes in phosphorylation were found in synapsins I and II at Ser-603, in CRMP2 at Ser-522 or Thr-514, in DARPP-32 at Thr-34, or in PDK1 at Ser-241. General levels of phosphorylation assessed with Pro-Q Diamond stain, or an anti-phosphotyrosine antibody, appeared similar in the WT and KO mice. We conclude that isoAsp accumulation is associated with altered functional status of several neuronal proteins that are highly susceptible to this type of damage. We also uncovered unexpected differences in how male and female mice respond to isoAsp accumulation in the brain.
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Affiliation(s)
- Zhenxia Qin
- Department of Molecular Biology & Biochemistry, University of California Irvine, Irvine, California, United States of America
| | - Rachel S. Kaufman
- Department of Molecular Biology & Biochemistry, University of California Irvine, Irvine, California, United States of America
| | - Rana N. Khoury
- Department of Molecular Biology & Biochemistry, University of California Irvine, Irvine, California, United States of America
| | - Mitri K. Khoury
- Department of Molecular Biology & Biochemistry, University of California Irvine, Irvine, California, United States of America
| | - Dana W. Aswad
- Department of Molecular Biology & Biochemistry, University of California Irvine, Irvine, California, United States of America
- * E-mail:
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Chen T, Nayak N, Majee SM, Lowenson J, Schäfermeyer KR, Eliopoulos AC, Lloyd TD, Dinkins R, Perry SE, Forsthoefel NR, Clarke SG, Vernon DM, Zhou ZS, Rejtar T, Downie AB. Substrates of the Arabidopsis thaliana protein isoaspartyl methyltransferase 1 identified using phage display and biopanning. J Biol Chem 2010; 285:37281-92. [PMID: 20870712 DOI: 10.1074/jbc.m110.157008] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The role of protein isoaspartyl methyltransferase (PIMT) in repairing a wide assortment of damaged proteins in a host of organisms has been inferred from the affinity of the enzyme for isoaspartyl residues in a plethora of amino acid contexts. The identification of PIMT target proteins in plant seeds, where the enzyme is highly active and proteome long-lived, has been hindered by large amounts of isoaspartate-containing storage proteins. Mature seed phage display libraries circumvented this problem. Inclusion of the PIMT co-substrate, S-adenosylmethionine (AdoMet), during panning permitted PIMT to retain aged phage in greater numbers than controls lacking co-substrate or when PIMT protein binding was poisoned with S-adenosyl homocysteine. After four rounds, phage titer plateaued in AdoMet-containing pans, whereas titer declined in both controls. This strategy identified 17 in-frame PIMT target proteins, including a cupin-family protein similar to those identified previously using on-blot methylation. All recovered phage had at least one susceptible Asp or Asn residue. Five targets were recovered independently. Two in-frame targets were produced in Escherichia coli as recombinant proteins and shown by on-blot methylation to acquire isoAsp, becoming a PIMT target. Both gained isoAsp rapidly in solution upon thermal insult. Mutant analysis of plants deficient in any of three in-frame PIMT targets resulted in demonstrable phenotypes. An over-representation of clones encoding proteins involved in protein production suggests that the translational apparatus comprises a subgroup for which PIMT-mediated repair is vital for orthodox seed longevity. Impaired PIMT activity would hinder protein function in these targets, possibly resulting in poor seed performance.
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Affiliation(s)
- Tingsu Chen
- Department of Horticulture, University of Kentucky, Lexington, Kentucky 40546-0312, USA
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