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Koff M, Monagas-Valentin P, Novikov B, Chandel I, Panin V. Protein O-mannosylation: one sugar, several pathways, many functions. Glycobiology 2023; 33:911-926. [PMID: 37565810 PMCID: PMC10859634 DOI: 10.1093/glycob/cwad067] [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: 07/16/2023] [Revised: 07/23/2023] [Accepted: 07/31/2023] [Indexed: 08/12/2023] Open
Abstract
Recent research has unveiled numerous important functions of protein glycosylation in development, homeostasis, and diseases. A type of glycosylation taking the center stage is protein O-mannosylation, a posttranslational modification conserved in a wide range of organisms, from yeast to humans. In animals, protein O-mannosylation plays a crucial role in the nervous system, whereas protein O-mannosylation defects cause severe neurological abnormalities and congenital muscular dystrophies. However, the molecular and cellular mechanisms underlying protein O-mannosylation functions and biosynthesis remain not well understood. This review outlines recent studies on protein O-mannosylation while focusing on the functions in the nervous system, summarizes the current knowledge about protein O-mannosylation biosynthesis, and discusses the pathologies associated with protein O-mannosylation defects. The evolutionary perspective revealed by studies in the Drosophila model system are also highlighted. Finally, the review touches upon important knowledge gaps in the field and discusses critical questions for future research on the molecular and cellular mechanisms associated with protein O-mannosylation functions.
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Affiliation(s)
- Melissa Koff
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
| | - Pedro Monagas-Valentin
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
| | - Boris Novikov
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
| | - Ishita Chandel
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
| | - Vladislav Panin
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
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Jiang H, Feng Y, He G, Liu Y, Li X. Analysis of the expression and distribution of protein O-linked mannose β1,2- N-acetylglucosaminyltransferase 1 in the normal adult mouse brain. Front Neuroanat 2023; 16:1043924. [PMID: 36686576 PMCID: PMC9853526 DOI: 10.3389/fnana.2022.1043924] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Accepted: 12/13/2022] [Indexed: 01/07/2023] Open
Abstract
Introduction Protein O-linked mannose β1,2-N-acetylglucosaminyltransferase 1 (POMGNT1) is crucial for the elongation of O-mannosyl glycans. Mutations in POMGNT1 cause muscle-eye-brain (MEB) disease, one of the main features of which is anatomical aberrations in the brain. A growing number of studies have shown that defects in POMGNT1 affect neuronal migration and distribution, disrupt basement membranes, and misalign Cajal-Retzius cells. Several studies have examined the distribution and expression of POMGNT1 in the fetal or neonatal brain for neurodevelopmental studies in the mouse or human brain. However, little is known about the neuroanatomical distribution and expression of POMGNT1 in the normal adult mouse brain. Methods We analyzed the expression of POMGNT1 mRNA and protein in the brains of various neuroanatomical regions and spinal cords by western blotting and RT-qPCR. We also detected the distribution profile of POMGnT1 in normal adult mouse brains by immunohistochemistry and double-immunofluorescence. Results In the present study, we found that POMGNT1-positive cells were widely distributed in various regions of the brain, with high levels of expression in the cerebral cortex and hippocampus. In terms of cell type, POMGNT1 was predominantly expressed in neurons and was mainly enriched in glutamatergic neurons; to a lesser extent, it was expressed in glial cells. At the subcellular level, POMGNT1 was mainly co-localized with the Golgi apparatus, but expression in the endoplasmic reticulum and mitochondria could not be excluded. Discussion The present study suggests that POMGNT1, although widely expressed in various brain regions, may has some regional and cellular specificity, and the outcomes of this study provide a new laboratory basis for revealing the possible involvement of POMGNT1 in normal physiological functions of the brain from a morphological perspective.
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Affiliation(s)
- Hanxiao Jiang
- Department of Neurology, The Second Affiliated Hospital of Chongqing Medical University, Chongqing, China
| | - Yuxue Feng
- Department of Neurology, The Second Affiliated Hospital of Chongqing Medical University, Chongqing, China
| | - Guiqiong He
- Chongqing Key Laboratory of Neurobiology, Chongqing Medical University, Chongqing, China,Department of Anatomy, Chongqing Medical University, Chongqing, China
| | - Yuanjie Liu
- Chongqing Key Laboratory of Neurobiology, Chongqing Medical University, Chongqing, China,Department of Anatomy, Chongqing Medical University, Chongqing, China,*Correspondence: Yuanjie Liu,
| | - Xiaofeng Li
- Department of Neurology, The Second Affiliated Hospital of Chongqing Medical University, Chongqing, China,Xiaofeng Li,
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Rab11-mediated post-Golgi transport of the sialyltransferase ST3GAL4 suggests a new mechanism for regulating glycosylation. J Biol Chem 2021; 296:100354. [PMID: 33524390 PMCID: PMC7949161 DOI: 10.1016/j.jbc.2021.100354] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Revised: 01/20/2021] [Accepted: 01/27/2021] [Indexed: 02/06/2023] Open
Abstract
Glycosylation, the most common posttranslational modification of proteins, is a stepwise process that relies on tight regulation of subcellular glycosyltransferase location to control the addition of each monosaccharide. Glycosyltransferases primarily reside and function in the endoplasmic reticulum (ER) and the Golgi apparatus; whether and how they traffic beyond the Golgi, how this trafficking is controlled, and how it impacts glycosylation remain unclear. Our previous work identified a connection between N-glycosylation and Rab11, a key player in the post-Golgi transport that connects recycling endosomes and other compartments. To learn more about the specific role of Rab11, we knocked down Rab11 in HeLa cells. Our findings indicate that Rab11 knockdown results in a dramatic enhancement in the sialylation of N-glycans. Structural analyses of glycans using lectins and LC-MS revealed that α2,3-sialylation is selectively enhanced, suggesting that an α2,3-sialyltransferase that catalyzes the sialyation of glycoproteins is activated or upregulated as the result of Rab11 knockdown. ST3GAL4 is the major α2,3-sialyltransferase that acts on N-glycans; we demonstrated that the localization of ST3GAL4, but not the levels of its mRNA, protein, or donor substrate, was altered by Rab11 depletion. In knockdown cells, ST3GAL4 is densely distributed in the trans-Golgi network, compared with the wider distribution in the Golgi and in other peripheral puncta in control cells, whereas the α2,6-sialyltransferase ST6GAL1 is predominantly localized to the Golgi regardless of Rab11 knockdown. This indicates that Rab11 may negatively regulate α2,3-sialylation by transporting ST3GAL4 to post-Golgi compartments (PGCs), which is a novel mechanism of glycosyltransferase regulation.
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Borgert A, Foley BL, Live D. Contrasting the conformational effects of α-O-GalNAc and α-O-Man glycan protein modifications and their impact on the mucin-like region of alpha-dystroglycan. Glycobiology 2020; 31:649-661. [PMID: 33295623 DOI: 10.1093/glycob/cwaa112] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 11/19/2020] [Accepted: 12/03/2020] [Indexed: 12/14/2022] Open
Abstract
We have carried out a comparative study of the conformational impact of modifications to threonine residues of either α-O-Man or α-O-GalNAc in the context of a sequence from the mucin-like region of α-dystroglycan. Both such modifications can coexist in this domain of the glycoprotein. Solution NMR experiments and molecular dynamics calculations were employed. Comparing the results for an unmodified peptide Ac- PPTTTTKKP-NH2 sequence from α-dystroglycan, and glycoconjugates with either modification on the Ts, we find that the impact of the α-O-Man modification on the peptide scaffold is quite limited, while that of the α-O-GalNAc is more profound. The results for the α-O-GalNAc glycoconjugate are consistent with what has been seen earlier in other systems. Further examination of the NMR-based structure and the MD results suggest a more extensive network of hydrogen bond interactions within the α-O-GalNAc-threonine residue than has been previously appreciated, which influences the properties of the protein backbone. The conformational effects are relevant to the mechanical properties of α-dystroglycan.
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Affiliation(s)
- Andrew Borgert
- Department of Medical Research, Gundersen Health System, 1900 South Ave., La Crosse, WI 54601, USA
| | - B Lachele Foley
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, USA
| | - David Live
- Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, USA
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Herbomel GG, Rojas RE, Tran DT, Ajinkya M, Beck L, Tabak LA. The GalNAc-T Activation Pathway (GALA) is not a general mechanism for regulating mucin-type O-glycosylation. PLoS One 2017; 12:e0179241. [PMID: 28719662 PMCID: PMC5515409 DOI: 10.1371/journal.pone.0179241] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Accepted: 05/25/2017] [Indexed: 12/03/2022] Open
Abstract
Mucin-type O-glycosylation is initiated by the UDP-GalNAc polypeptide:N-acetylgalactosaminyltransferase (GalNAc-T) family of enzymes. Their activity results in the GalNAc α1-O-Thr/Ser structure, termed the Tn antigen, which is further decorated with additional sugars. In neoplastic cells, the Tn antigen is often overexpressed. Because O-glycosylation is controlled by the activity of GalNAc-Ts, their regulation is of great interest. Previous reports suggest that growth factors, EGF or PDGF, induce Golgi complex-to-endoplasmic reticulum (ER) relocation of both GalNAc-Ts and Tn antigen in HeLa cells, offering a mechanism for Tn antigen overexpression termed "GALA". However, we were unable to reproduce these findings. Upon treatment of HeLa cells with either EGF or PDGF we observed no change in the co-localization of endogenous GalNAc-T1, GalNAc-T2 or Tn antigen with the Golgi complex marker TGN46. There was also no enhancement of localization with the ER marker calnexin. We conclude that growth factors do not cause redistribution of GalNAc-Ts from the Golgi complex to the ER in HeLa cells.
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Affiliation(s)
- Gaetan G. Herbomel
- Section on Biological Chemistry, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Raul E. Rojas
- Section on Biological Chemistry, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Duy T. Tran
- Section on Biological Chemistry, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Monica Ajinkya
- Section on Biological Chemistry, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Lauren Beck
- Section on Biological Chemistry, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Lawrence A. Tabak
- Section on Biological Chemistry, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, United States of America
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Larsen ISB, Narimatsu Y, Joshi HJ, Yang Z, Harrison OJ, Brasch J, Shapiro L, Honig B, Vakhrushev SY, Clausen H, Halim A. Mammalian O-mannosylation of cadherins and plexins is independent of protein O-mannosyltransferases 1 and 2. J Biol Chem 2017; 292:11586-11598. [PMID: 28512129 DOI: 10.1074/jbc.m117.794487] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Indexed: 11/06/2022] Open
Abstract
Protein O-mannosylation is found in yeast and metazoans, and a family of conserved orthologous protein O-mannosyltransferases is believed to initiate this important post-translational modification. We recently discovered that the cadherin superfamily carries O-linked mannose (O-Man) glycans at highly conserved residues in specific extracellular cadherin domains, and it was suggested that the function of E-cadherin was dependent on the O-Man glycans. Deficiencies in enzymes catalyzing O-Man biosynthesis, including the two human protein O-mannosyltransferases, POMT1 and POMT2, underlie a subgroup of congenital muscular dystrophies designated α-dystroglycanopathies, because deficient O-Man glycosylation of α-dystroglycan disrupts laminin interaction with α-dystroglycan and the extracellular matrix. To explore the functions of O-Man glycans on cadherins and protocadherins, we used a combinatorial gene-editing strategy in multiple cell lines to evaluate the role of the two POMTs initiating O-Man glycosylation and the major enzyme elongating O-Man glycans, the protein O-mannose β-1,2-N-acetylglucosaminyltransferase, POMGnT1. Surprisingly, O-mannosylation of cadherins and protocadherins does not require POMT1 and/or POMT2 in contrast to α-dystroglycan, and moreover, the O-Man glycans on cadherins are not elongated. Thus, the classical and evolutionarily conserved POMT O-mannosylation pathway is essentially dedicated to α-dystroglycan and a few other proteins, whereas a novel O-mannosylation process in mammalian cells is predicted to serve the large cadherin superfamily and other proteins.
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Affiliation(s)
- Ida Signe Bohse Larsen
- From the Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark, and
| | - Yoshiki Narimatsu
- From the Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark, and
| | - Hiren Jitendra Joshi
- From the Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark, and
| | - Zhang Yang
- From the Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark, and
| | | | - Julia Brasch
- the Department of Biochemistry and Molecular Biophysics
| | - Lawrence Shapiro
- the Department of Biochemistry and Molecular Biophysics.,Zuckerman Mind Brain Behavior Institute, Department of Systems Biology, and
| | - Barry Honig
- the Department of Biochemistry and Molecular Biophysics.,Zuckerman Mind Brain Behavior Institute, Department of Systems Biology, and.,Howard Hughes Medical Institute Columbia University, New York, New York 10032
| | - Sergey Y Vakhrushev
- From the Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark, and
| | - Henrik Clausen
- From the Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark, and
| | - Adnan Halim
- From the Copenhagen Center for Glycomics, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark, and
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Harvey DJ. Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012. MASS SPECTROMETRY REVIEWS 2017; 36:255-422. [PMID: 26270629 DOI: 10.1002/mas.21471] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Accepted: 01/15/2015] [Indexed: 06/04/2023]
Abstract
This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.
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Affiliation(s)
- David J Harvey
- Department of Biochemistry, Oxford Glycobiology Institute, University of Oxford, Oxford, OX1 3QU, UK
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The Structure of the T190M Mutant of Murine α-Dystroglycan at High Resolution: Insight into the Molecular Basis of a Primary Dystroglycanopathy. PLoS One 2015; 10:e0124277. [PMID: 25932631 PMCID: PMC4416926 DOI: 10.1371/journal.pone.0124277] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Accepted: 03/12/2015] [Indexed: 11/19/2022] Open
Abstract
The severe dystroglycanopathy known as a form of limb-girdle muscular dystrophy (LGMD2P) is an autosomal recessive disease caused by the point mutation T192M in α-dystroglycan. Functional expression analysis in vitro and in vivo indicated that the mutation was responsible for a decrease in posttranslational glycosylation of dystroglycan, eventually interfering with its extracellular-matrix receptor function and laminin binding in skeletal muscle and brain. The X-ray crystal structure of the missense variant T190M of the murine N-terminal domain of α-dystroglycan (50-313) has been determined, and showed an overall topology (Ig-like domain followed by a basket-shaped domain reminiscent of the small subunit ribosomal protein S6) very similar to that of the wild-type structure. The crystallographic analysis revealed a change of the conformation assumed by the highly flexible loop encompassing residues 159-180. Moreover, a solvent shell reorganization around Met190 affects the interaction between the B1-B5 anti-parallel strands forming part of the floor of the basket-shaped domain, with likely repercussions on the folding stability of the protein domain(s) and on the overall molecular flexibility. Chemical denaturation and limited proteolysis experiments point to a decreased stability of the T190M variant with respect to its wild-type counterpart. This mutation may render the entire L-shaped protein architecture less flexible. The overall reduced flexibility and stability may affect the functional properties of α-dystroglycan via negatively influencing its binding behavior to factors needed for dystroglycan maturation, and may lay the molecular basis of the T190M-driven primary dystroglycanopathy.
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Praissman JL, Wells L. Mammalian O-mannosylation pathway: glycan structures, enzymes, and protein substrates. Biochemistry 2014; 53:3066-78. [PMID: 24786756 PMCID: PMC4033628 DOI: 10.1021/bi500153y] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The
mammalian O-mannosylation pathway for protein post-translational
modification is intricately involved in modulating cell–matrix
interactions in the musculature and nervous system. Defects in enzymes
of this biosynthetic pathway are causative for multiple forms of congenital
muscular dystophy. The application of advanced genetic and biochemical
technologies has resulted in remarkable progress in this field over
the past few years, culminating with the publication of three landmark
papers in 2013 alone. In this review, we will highlight recent progress
focusing on the dramatic expansion of the set of genes known to be
involved in O-mannosylation and disease processes, the concurrent
acceleration of the rate of O-mannosylation pathway protein functional
assignments, the tremendous increase in the number of proteins now
known to be modified by O-mannosylation, and the recent progress in
protein O-mannose glycan quantification and site assignment. Also,
we attempt to highlight key outstanding questions raised by this abundance
of new information.
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Affiliation(s)
- Jeremy L Praissman
- Complex Carbohydrate Research Center, Department of Biochemistry and Molecular Biology, The University of Georgia , Athens, Georgia 30602, United States
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Panin VM, Wells L. Protein O-mannosylation in metazoan organisms. CURRENT PROTOCOLS IN PROTEIN SCIENCE 2014; 75:12.12.1-12.12.29. [PMID: 24510673 PMCID: PMC3984005 DOI: 10.1002/0471140864.ps1212s75] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Protein O-mannosylation is a special type of glycosylation that plays prominent roles in metazoans, affecting development and physiology of the nervous system and muscles. A major biological effect of O-mannosylation involves the regulation of α-dystroglycan, a membrane glycoprotein mediating cell-extracellular matrix interactions. Genetic defects of O-mannosylation result in the loss of ligand-binding activity of α-dystroglycan and cause congenital muscular dystrophies termed dystroglycanopathies. Recent progress in mass spectrometry and in vitro analyses has shed new light on the mechanism of α-dystroglycan glycosylation; however, this mechanism is underlain by complex genetic and molecular elements that remain poorly understood. Protein O-mannosylation is evolutionarily conserved in metazoans, yet the pathway is simplified and more amenable to genetic analyses in invertebrate organisms, indicating that genetically tractable in vivo models could facilitate research in this area. This unit describes recent methodological strategies for studying protein O-mannosylation using in vitro and in vivo approaches.
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Affiliation(s)
- Vladislav M. Panin
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843; Tel. 979-458-4630, FAX 979-845-9274
| | - Lance Wells
- Complex Carbohydrate Research Center, Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602; Tel 706-542-7806, FAX 706-542-4412
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Parkinson W, Dear ML, Rushton E, Broadie K. N-glycosylation requirements in neuromuscular synaptogenesis. Development 2013; 140:4970-81. [PMID: 24227656 DOI: 10.1242/dev.099192] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Neural development requires N-glycosylation regulation of intercellular signaling, but the requirements in synaptogenesis have not been well tested. All complex and hybrid N-glycosylation requires MGAT1 (UDP-GlcNAc:α-3-D-mannoside-β1,2-N-acetylglucosaminyl-transferase I) function, and Mgat1 nulls are the most compromised N-glycosylation condition that survive long enough to permit synaptogenesis studies. At the Drosophila neuromuscular junction (NMJ), Mgat1 mutants display selective loss of lectin-defined carbohydrates in the extracellular synaptomatrix, and an accompanying accumulation of the secreted endogenous Mind the gap (MTG) lectin, a key synaptogenesis regulator. Null Mgat1 mutants exhibit strongly overelaborated synaptic structural development, consistent with inhibitory roles for complex/hybrid N-glycans in morphological synaptogenesis, and strengthened functional synapse differentiation, consistent with synaptogenic MTG functions. Synapse molecular composition is surprisingly selectively altered, with decreases in presynaptic active zone Bruchpilot (BRP) and postsynaptic Glutamate receptor subtype B (GLURIIB), but no detectable change in a wide range of other synaptic components. Synaptogenesis is driven by bidirectional trans-synaptic signals that traverse the glycan-rich synaptomatrix, and Mgat1 mutation disrupts both anterograde and retrograde signals, consistent with MTG regulation of trans-synaptic signaling. Downstream of intercellular signaling, pre- and postsynaptic scaffolds are recruited to drive synaptogenesis, and Mgat1 mutants exhibit loss of both classic Discs large 1 (DLG1) and newly defined Lethal (2) giant larvae [L(2)GL] scaffolds. We conclude that MGAT1-dependent N-glycosylation shapes the synaptomatrix carbohydrate environment and endogenous lectin localization within this domain, to modulate retention of trans-synaptic signaling ligands driving synaptic scaffold recruitment during synaptogenesis.
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Affiliation(s)
- William Parkinson
- Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37212, USA
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Live D, Wells L, Boons GJ. Dissecting the molecular basis of the role of the O-mannosylation pathway in disease: α-dystroglycan and forms of muscular dystrophy. Chembiochem 2013; 14:2392-402. [PMID: 24318691 DOI: 10.1002/cbic.201300417] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Indexed: 11/10/2022]
Abstract
Dystroglycanopathies form a subgroup of muscular dystrophies that arise from defects in enzymes that are implicated in the recently elucidated O-mannosylation pathway, thereby resulting in underglycosylation of α-dystroglycan. The emerging identification of additional brain proteins modified by O-mannosylation provides a broader context for interpreting the range of neurological consequences associated with dystroglycanopathies. This form of glycosylation is associated with protein mucin-like domains that present numerous serine and threonine residues as possible sites for modification. Furthermore, the O-Man glycans coexist in this region with O-GalNAc glycans (conventionally associated with such protein sequences), thus resulting in a complex glycoconjugate landscape. Sorting out the relationships between the various molecular defects in glycosylation and the modes of disease presentation, as well as the regulatory interplay among the O-Man glycans and the effects on other modes of glycosylation in the same domain, is challenging. Here we provide a perspective on chemical biology approaches employing synthetic and analytical methods to address these questions.
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Affiliation(s)
- David Live
- Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 (USA)
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Bozzi M, Di Stasio E, Scaglione GL, Desiderio C, Martelli C, Giardina B, Sciandra F, Brancaccio A. Probing the stability of the "naked" mucin-like domain of human α-dystroglycan. BMC BIOCHEMISTRY 2013; 14:15. [PMID: 23815856 PMCID: PMC3704865 DOI: 10.1186/1471-2091-14-15] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Accepted: 06/20/2013] [Indexed: 11/10/2022]
Abstract
Background α-Dystroglycan (α-DG) is heavily glycosylated within its central mucin-like domain. The glycosylation shell of α-dystroglycan is known to largely influence its functional properties toward extracellular ligands. The structural features of this α-dystroglycan domain have been poorly studied so far. For the first time, we have attempted a recombinant expression approach in E. coli cells, in order to analyze by biochemical and biophysical techniques this important domain of the α-dystroglycan core protein. Results We expressed the recombinant mucin-like domain of human α-dystroglycan in E. coli cells, and purified it as a soluble peptide of 174 aa. A cleavage event, that progressively emerges under repeated cycles of freeze/thaw, occurs at the carboxy side of Arg461, liberating a 151 aa fragment as revealed by mass spectrometry analysis. The mucin-like peptide lacks any particular fold, as confirmed by its hydrodynamic properties and its fluorescence behavior under guanidine hydrochloride denaturation. Dynamic light scattering has been used to demonstrate that this mucin-like peptide is arranged in a conformation that is prone to aggregation at room temperature, with a melting temperature of ~40°C, which indicates a pronounced instability. Such a conclusion has been corroborated by trypsin limited proteolysis, upon which the protein has been fully degraded in less than 60 min. Conclusions Our analysis indirectly confirms the idea that the mucin-like domain of α-dystroglycan needs to be extensively glycosylated in order to reach a stable conformation. The absence/reduction of glycosylation by itself may greatly reduce the stability of the dystroglycan complex. Although an altered pattern of α-dystroglycan O-mannosylation, that is not significantly changing its overall glycosylation fraction, represents the primary molecular clue behind currently known dystroglycanopathies, it cannot be ruled out that still unidentified forms of αDG-related dystrophy might originate by a more substantial reduction of α-dystroglycan glycosylation and by its consequent destabilization.
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Wells L. The o-mannosylation pathway: glycosyltransferases and proteins implicated in congenital muscular dystrophy. J Biol Chem 2013; 288:6930-5. [PMID: 23329833 DOI: 10.1074/jbc.r112.438978] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Several forms of congenital muscular dystrophy, referred to as dystroglycanopathies, result from defects in the protein O-mannosylation biosynthetic pathway. In this minireview, I discuss 12 proteins involved in the pathway and how they play a role in the building of glycan structures (most notably on the protein α-dystroglycan) that allow for binding to multiple proteins of the extracellular matrix.
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Affiliation(s)
- Lance Wells
- Complex Carbohydrate Research Center and Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, USA
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Gomez Toledo A, Raducu M, Cruces J, Nilsson J, Halim A, Larson G, Rüetschi U, Grahn A. O-Mannose and O-N-acetyl galactosamine glycosylation of mammalian α-dystroglycan is conserved in a region-specific manner. Glycobiology 2012; 22:1413-23. [PMID: 22781125 DOI: 10.1093/glycob/cws109] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Defects in the O-linked glycosylation of the peripheral membrane protein α-dystroglycan (α-DG) are the main cause of several forms of congenital muscular dystrophies and thus the characterization of the glycosylation of α-DG is of great medical importance. A detailed investigation of the glycosylation pattern of the native α-DG protein is essential for the understanding of the biological processes related to human disease in which the protein is involved. To date, several studies have reported novel O-glycans and attachment sites on the mucin-like domain of mammalian α-DG with both similar and contradicting glycosylation patterns, indicating the species-specific O-glycosylation of mammalian α-DG. By applying a standardized purification scheme and subsequent glycoproteomic analysis of native α-DG from rabbit and human skeletal muscle biopsies and from cultured mouse C2C12 myotubes, we show that the O-glycosylation patterns of the mucin-like domain of native α-DG are conserved among mammalians in a region-specific manner.
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Affiliation(s)
- Alejandro Gomez Toledo
- Department of Clinical Chemistry and Transfusion Medicine, Institute of Biomedicine, Sahlgrenska Academy at the University of Gothenburg, Sahlgrenska University Hospital, Göteborg, Sweden
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Ding MX, Wang HF, Wang JS, Zhan H, Zuo YG, Yang DL, Liu JY, Wang W, Ke CX, Yan RP. ppGalNAc T1 as a potential novel marker for human bladder cancer. Asian Pac J Cancer Prev 2012; 13:5653-7. [PMID: 23317233 DOI: 10.7314/apjcp.2012.13.11.5653] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
OBJECTIVES To investigate the effect of glycopeptide-preferring polypeptide GalNAc transferase 1 (ppGalNAc T1) targeted RNA interference (RNAi) on the growth and migration of human bladder carcinoma EJ cells in vitro and in vivo. METHODS DNA microarray assays were performed to determine ppGalNAc Ts(ppGalNAc T1-9) expression in human bladder cancer and normal bladder tissues. We transfected the EJ bladder cancer cell line with well-designed ppGalNAc T1 siRNA. Boyden chamber and Wound healing assays were used to investigate changes of shppGalNAc T1-EJ cell migration. Proliferation of shppGalNAc T1-EJ cells in vitro was assessed using [3H]-thymidine incorporation assay and soft agar colony formation assays. Subcutaneous bladder tumors in BALB/c nude mice were induced by inoculation of shppGalNAc T1-EJ cells and after inoculation diameters of tumors were measured every 5 days to determine gross tumor volumes. RESULTS ppGalNAc T1 mRNA in bladder cancer tissues was 11.2-fold higher than in normal bladder tissues. When ppGalNAc T1 expression in EJ cells was knocked down through transfection by pSUPER-shppGalNAc T1 vector, markedly reduced incorporation of [3H]-thymidine into DNA of EJ cells was observed at all time points compared with the empty vector transfected control cells. However, ppGalNAc T1 knockdown did not significantly inhibited cell migration (only 12.3%). Silenced ppGalNAc T1 expression significantly inhibited subcutaneous tumor growth compared with the control groups injected with empty vector transfected control cells. At the end of observation course (40 days), the inhibitory rate of cancerous growth for ppGalNAc T1 knockdown was 52.5%. CONCLUSION ppGalNAc T1 might be a potential novel marker for human bladder cancer. Although ppGalNAc T1 knockdown caused no remarkable change in cell migration, silenced expression significantly inhibited proliferation and tumor growth of the bladder cancer EJ cell line.
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Affiliation(s)
- Ming-Xia Ding
- Department of Urology, The Second Affiliated Hospital of Kunming Medical University, Yunnan Institute of Urology, Kunming, China E-mail :
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