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Hasegawa H, Wang S, Kast E, Chou HT, Kaur M, Janlaor T, Mostafavi M, Wang YL, Li P. Understanding the biosynthesis of human IgM SAM-6 through a combinatorial expression of mutant subunits that affect product assembly and secretion. PLoS One 2024; 19:e0291568. [PMID: 38848420 PMCID: PMC11161108 DOI: 10.1371/journal.pone.0291568] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Accepted: 05/06/2024] [Indexed: 06/09/2024] Open
Abstract
Polymeric IgMs are secreted from plasma cells abundantly despite their structural complexity and intricate multimerization steps. To gain insights into IgM's assembly mechanics that underwrite such high-level secretion, we characterized the biosynthetic process of a natural human IgM, SAM-6, using a heterologous HEK293(6E) cell platform that allowed the production of IgMs both in hexameric and pentameric forms in a controlled fashion. By creating a series of mutant subunits that differentially disrupt secretion, folding, and specific inter-chain disulfide bond formation, we assessed their effects on various aspects of IgM biosynthesis in 57 different subunit chain combinations, both in hexameric and pentameric formats. The mutations caused a spectrum of changes in steady-state subcellular subunit distribution, ER-associated inclusion body formation, intracellular subunit detergent solubility, covalent assembly, secreted IgM product quality, and secretion output. Some mutations produced differential effects on product quality depending on whether the mutation was introduced to hexameric IgM or pentameric IgM. Through this systematic combinatorial approach, we consolidate diverse overlapping knowledge on IgM biosynthesis for both hexamers and pentamers, while unexpectedly revealing that the loss of certain inter-chain disulfide bonds, including the one between μHC and λLC, is tolerated in polymeric IgM assembly and secretion. The findings highlight the differential roles of underlying non-covalent protein-protein interactions in hexamers and pentamers when orchestrating the initial subunit interactions and maintaining the polymeric IgM product integrity during ER quality control steps, secretory pathway trafficking, and secretion.
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Affiliation(s)
- Haruki Hasegawa
- Discovery Protein Science, Department of Large Molecule Discovery and Research Data Science, Amgen Inc., South San Francisco, CA, United States of America
| | - Songyu Wang
- Discovery Protein Science, Department of Large Molecule Discovery and Research Data Science, Amgen Inc., South San Francisco, CA, United States of America
| | - Eddie Kast
- Molecular Analytics, Department of Biologic Therapeutic Discovery, Amgen Inc., South San Francisco, CA, United States of America
| | - Hui-Ting Chou
- Structural Biology, Department of Small Molecule Therapeutic Discovery, Amgen Inc., South San Francisco, CA, United States of America
| | - Mehma Kaur
- Discovery Protein Science, Department of Large Molecule Discovery and Research Data Science, Amgen Inc., South San Francisco, CA, United States of America
| | - Tanakorn Janlaor
- Discovery Protein Science, Department of Large Molecule Discovery and Research Data Science, Amgen Inc., South San Francisco, CA, United States of America
| | - Mina Mostafavi
- Discovery Protein Science, Department of Large Molecule Discovery and Research Data Science, Amgen Inc., South San Francisco, CA, United States of America
| | - Yi-Ling Wang
- Discovery Protein Science, Department of Large Molecule Discovery and Research Data Science, Amgen Inc., South San Francisco, CA, United States of America
| | - Peng Li
- Discovery Protein Science, Department of Large Molecule Discovery and Research Data Science, Amgen Inc., South San Francisco, CA, United States of America
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2
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Lim S, Kwon HJ, Jeong DG, Nie H, Lee S, Ko SR, Lee KS, Ryu YB, Mason HS, Kim HS, Shin AY, Kwon SY. Enhanced binding and inhibition of SARS-CoV-2 by a plant-derived ACE2 protein containing a fused mu tailpiece. Biotechnol J 2024; 19:e2300319. [PMID: 37853601 DOI: 10.1002/biot.202300319] [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: 06/30/2023] [Revised: 09/27/2023] [Accepted: 10/11/2023] [Indexed: 10/20/2023]
Abstract
Infectious diseases such as Coronavirus disease 2019 (COVID-19) and Middle East respiratory syndrome (MERS) present an increasingly persistent crisis in many parts of the world. COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The angiotensin-converting enzyme 2 (ACE2) is a crucial cellular receptor for SARS-CoV-2 infection. Inhibition of the interaction between SARS-CoV-2 and ACE2 has been proposed as a target for the prevention and treatment of COVID-19. We produced four recombinant plant-derived ACE2 isoforms with or without the mu tailpiece (μ-tp) of immunoglobulin M (IgM) and the KDEL endoplasmic reticulum retention motif in a plant expression system. The plant-derived ACE2 isoforms bound whole SARS-CoV-2 virus and the isolated receptor binding domains of SARS-CoV-2 Alpha, Beta, Gamma, Delta, and Omicron variants. Fusion of μ-tp and KDEL to the ACE2 protein (ACE2 μK) had enhanced binding activity with SARS-CoV-2 in comparison with unmodified ACE2 protein derived from CHO cells. Furthermore, the plant-derived ACE2 μK protein exhibited no cytotoxic effects on Vero E6 cells and effectively inhibited SARS-CoV-2 infection. The efficient and rapid scalability of plant-derived ACE2 μK protein offers potential for the development of preventive and therapeutic agents in the early response to future viral outbreaks.
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Affiliation(s)
- Sohee Lim
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
| | - Hyung-Jun Kwon
- Functional Biomaterial Research Center, Korea Research Institute of Bioscience and Biotechnology, Jeongeup, Republic of Korea
| | - Dae Gwin Jeong
- Bionanotechnology Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
- Bio-Analytical Science Division, Korea Research Institute of Bioscience and Biotechnology School of Biotechnology, University of Science and Technology, Daejeon, Republic of Korea
| | - Hualin Nie
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
| | - Sanghee Lee
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
- Biosystems and Bioengineering Program, Korea Research Institute of Bioscience and Biotechnology School of Biotechnology, University of Science and Technology, Daejeon, Republic of Korea
| | - Seo-Rin Ko
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
- Department of Bioinformatics, Korea Research Institute of Bioscience and Biotechnology School of Bioscience, University of Science and Technology, Daejeon, Republic of Korea
| | - Kyu-Sun Lee
- Bionanotechnology Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
- Bio-Analytical Science Division, Korea Research Institute of Bioscience and Biotechnology School of Biotechnology, University of Science and Technology, Daejeon, Republic of Korea
| | - Young Bae Ryu
- Functional Biomaterial Research Center, Korea Research Institute of Bioscience and Biotechnology, Jeongeup, Republic of Korea
| | - Hugh S Mason
- Center for Immunotherapy, Vaccines, and Virotherapy (CIVV), The Biodesign Institute at ASU, Tempe, Arizona, USA
| | - Hyun-Soon Kim
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
- Biosystems and Bioengineering Program, Korea Research Institute of Bioscience and Biotechnology School of Biotechnology, University of Science and Technology, Daejeon, Republic of Korea
| | - Ah-Young Shin
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
- Department of Bioinformatics, Korea Research Institute of Bioscience and Biotechnology School of Bioscience, University of Science and Technology, Daejeon, Republic of Korea
| | - Suk-Yoon Kwon
- Plant Systems Engineering Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
- Biosystems and Bioengineering Program, Korea Research Institute of Bioscience and Biotechnology School of Biotechnology, University of Science and Technology, Daejeon, Republic of Korea
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Xu X, Delves PJ, Huang J, Shao W, Qiu X. Comparison of Non B-Ig and B-Ig. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2024; 1445:73-88. [PMID: 38967751 DOI: 10.1007/978-981-97-0511-5_6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/06/2024]
Abstract
Immunoglobulin (Ig) has been widely acknowledged to be produced solely by B-lineage cells. However, growing evidence has demonstrated the expression of Ig in an array of cancer cells, as well as normal cells including epithelial cells, epidermal cells, mesangial cells, monocytes, and neutrophils. Ig has even been found to be expressed in non-B cells at immune-privileged sites such as neurons and spermatogenic cells. Despite these non-B cell-derived Igs (non-B-Igs) sharing the same symmetric structures with conventional Igs (B-Igs), further studies have revealed unique characteristics of non-B-Ig, such as restricted variable region and aberrant glycosylation. Moreover, non-B-Ig exhibits properties of promoting malignant behaviours of cancer cells, therefore it could be utilised in the clinic as a potential therapeutic biomarker or target. The elucidation of the generation and regulation of non-B-Ig will certainly broaden our understanding of immunology.
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Affiliation(s)
- Xiaojun Xu
- Department of Immunology, School of Basic Medical Sciences, Peking University, Beijing, China.
| | - Peter J Delves
- Division of Infection and Immunity, Department of Immunology, UCL (University College London), London, UK
| | - Jing Huang
- Department of Immunology, School of Basic Medical Sciences, Peking University, Beijing, China
| | - Wenwei Shao
- Academy of Medical Engineering and Translational Medicine, Tianjin University, Tianjin, China
| | - Xiaoyan Qiu
- Department of Immunology, School of Basic Medical Sciences, Peking University, Beijing, China
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4
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Lyu M, Malyutin AG, Stadtmueller BM. The structure of the teleost Immunoglobulin M core provides insights on polymeric antibody evolution, assembly, and function. Nat Commun 2023; 14:7583. [PMID: 37989996 PMCID: PMC10663602 DOI: 10.1038/s41467-023-43240-z] [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: 03/15/2023] [Accepted: 11/04/2023] [Indexed: 11/23/2023] Open
Abstract
Polymeric (p) immunoglobulins (Igs) serve broad functions during vertebrate immune responses. Typically, pIgs contain between two and six Ig monomers, each with two antigen binding fragments and one fragment crystallization (Fc). In addition, many pIgs assemble with a joining-chain (JC); however, the number of monomers and potential to include JC vary with species and heavy chain class. Here, we report the cryo-electron microscopy structure of IgM from a teleost (t) species, which does not encode JC. The structure reveals four tIgM Fcs linked through eight C-terminal tailpieces (Tps), which adopt a single β-sandwich-like domain (Tp assembly) located between two Fcs. Specifically, two of eight heavy chains fold uniquely, resulting in a structure distinct from mammalian IgM, which typically contains five IgM monomers, one JC and a centrally-located Tp assembly. Together with mutational analysis, structural data indicate that pIgs have evolved a range of assembly mechanisms and structures, each likely to support unique antibody effector functions.
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Affiliation(s)
- Mengfan Lyu
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL, 61801, USA
| | - Andrey G Malyutin
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
- Beckman Institute, California Institute of Technology, Pasadena, CA, 91125, USA
- Takeda Pharmaceuticals, Cambridge, MA, 02139, USA
| | - Beth M Stadtmueller
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL, 61801, USA.
- Department of Biomedical and Translational Sciences, Carle Illinois College of Medicine, University of Illinois Urbana-Champaign, Urbana, IL, 61801, USA.
- Carl R. Woese Institute for Genomic Biology, University of Illinois Urbana-Champaign, Urbana, IL, 61801, USA.
- Center for Biophysics and Quantitative Biology, University of Illinois Urbana-Champaign, Urbana, IL, 61801, USA.
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5
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Lyu M, Malyutin AG, Stadtmueller BM. The structure of the teleost Immunoglobulin M core provides insights on polymeric antibody evolution, assembly, and function. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.29.534771. [PMID: 37034677 PMCID: PMC10081254 DOI: 10.1101/2023.03.29.534771] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Polymeric (p) immunoglobulins (Igs) serve broad functions during vertebrate immune responses. Typically, pIgs contain between two and six Ig monomers, each with two antigen binding fragments and one fragment crystallization (Fc). In addition, many pIgs assemble with a joining-chain (JC); however, the number of monomers and potential to include JC varies with species and heavy chain class. Here, we report the cryo-electron microscopy structure of IgM from a teleost (t) species, which does not encode JC. The structure revealed four tIgM Fcs linked through eight C-terminal tailpieces (Tps), which adopt a single β-sandwich-like domain (Tp assembly) located between two Fcs. Remarkably, two of eight heavy chains fold uniquely, resulting in a structure distinct from mammalian IgM, which typically contains five IgM monomers, one JC and a centrally-located Tp assembly. Together with mutational analysis, structural data indicate that pIgs have evolved a range of assembly mechanisms and structures, each likely to support unique antibody effector functions.
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Affiliation(s)
- Mengfan Lyu
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois 61801 USA
| | - Andrey G. Malyutin
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125 USA
- Beckman Institute, California Institute of Technology, Pasadena, CA 91125 USA
- Present address, Takeda Development Center Americas, San Diego, California 92121
| | - Beth M. Stadtmueller
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, Illinois 61801 USA
- Department of Biomedical and Translational Sciences, Carle Illinois College of Medicine, University of Illinois Urbana-Champaign, Urbana, Illinois 61801 USA
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6
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Multimeric ACE2-IgM fusions as broadly active antivirals that potently neutralize SARS-CoV-2 variants. Commun Biol 2022; 5:1237. [DOI: 10.1038/s42003-022-04193-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Accepted: 10/28/2022] [Indexed: 11/13/2022] Open
Abstract
AbstractCoronavirus infections are a world-wide threat to human health. A promising strategy to develop a broadly active antiviral is the use of fusion proteins consisting of an antibody IgG Fc region and a human ACE2 domain to which the viral spike proteins bind. Here we create antiviral fusion proteins based on IgM scaffolds. The hexameric ACE2-IgM-Fc fusions can be efficiently produced in mammalian cells and they neutralize the infectious virus with picomolar affinity thus surpassing monomeric ACE2-IgM-Fc by up to 96-fold in potency. In addition, the ACE2-IgM fusion shows increased neutralization efficiency for the highly infectious SARS-CoV-2 omicron variant in comparison to prototypic SARS-CoV-2. Taken together, these multimeric IgM fusions proteins are a powerful weapon to fight coronavirus infections.
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Vattepu R, Sneed SL, Anthony RM. Sialylation as an Important Regulator of Antibody Function. Front Immunol 2022; 13:818736. [PMID: 35464485 PMCID: PMC9021442 DOI: 10.3389/fimmu.2022.818736] [Citation(s) in RCA: 32] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2021] [Accepted: 03/17/2022] [Indexed: 12/14/2022] Open
Abstract
Antibodies play a critical role in linking the adaptive immune response to the innate immune system. In humans, antibodies are categorized into five classes, IgG, IgM, IgA, IgE, and IgD, based on constant region sequence, structure, and tropism. In serum, IgG is the most abundant antibody, comprising 75% of antibodies in circulation, followed by IgA at 15%, IgM at 10%, and IgD and IgE are the least abundant. All human antibody classes are post-translationally modified by sugars. The resulting glycans take on many divergent structures and can be attached in an N-linked or O-linked manner, and are distinct by antibody class, and by position on each antibody. Many of these glycan structures on antibodies are capped by sialic acid. It is well established that the composition of the N-linked glycans on IgG exert a profound influence on its effector functions. However, recent studies have described the influence of glycans, particularly sialic acid for other antibody classes. Here, we discuss the role of glycosylation, with a focus on terminal sialylation, in the biology and function across all antibody classes. Sialylation has been shown to influence not only IgG, but IgE, IgM, and IgA biology, making it an important and unappreciated regulator of antibody function.
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Affiliation(s)
- Ravi Vattepu
- Center for Immunology and Inflammatory Diseases, Division of Rheumatology, Allergy and Immunology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
| | - Sunny Lyn Sneed
- Center for Immunology and Inflammatory Diseases, Division of Rheumatology, Allergy and Immunology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
| | - Robert M Anthony
- Center for Immunology and Inflammatory Diseases, Division of Rheumatology, Allergy and Immunology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
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8
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Giannone C, Chelazzi MR, Orsi A, Anelli T, Nguyen T, Buchner J, Sitia R. Biogenesis of secretory immunoglobulin M requires intermediate non-native disulfide bonds and engagement of the protein disulfide isomerase ERp44. EMBO J 2022; 41:e108518. [PMID: 34957576 PMCID: PMC8804937 DOI: 10.15252/embj.2021108518] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 11/13/2021] [Accepted: 11/25/2021] [Indexed: 02/03/2023] Open
Abstract
Antibodies of the immunoglobulin M (IgM) class represent the frontline of humoral immune responses. They are secreted as planar polymers in which flanking µ2 L2 "monomeric" subunits are linked by two disulfide bonds, one formed by the penultimate cysteine (C575) in the tailpiece of secretory µ chains (µs tp) and the second by C414 in the Cµ3. The latter bond is not present in membrane IgM. Here, we show that C575 forms a non-native, intra-subunit disulfide bond as a key step in the biogenesis of secretory IgM. The abundance of this unexpected intermediate correlates with the onset and extent of polymerization. The rearrangement of the C-terminal tails into a native quaternary structure is guaranteed by the engagement of protein disulfide isomerase ERp44, which attacks the non-native C575 bonds. The resulting conformational changes promote polymerization and formation of C414 disulfide linkages. This unusual assembly pathway allows secretory polymers to form without the risk of disturbing the role of membrane IgM as part of the B cell antigen receptor.
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Affiliation(s)
- Chiara Giannone
- Division of Genetics and Cell BiologyUniversità Vita‐Salute IRCCS Ospedale San RaffaeleMilanoItaly
- Vita‐Salute San Raffaele UniversityMilanItaly
| | - Maria Rita Chelazzi
- Division of Genetics and Cell BiologyUniversità Vita‐Salute IRCCS Ospedale San RaffaeleMilanoItaly
- Vita‐Salute San Raffaele UniversityMilanItaly
| | - Andrea Orsi
- Division of Genetics and Cell BiologyUniversità Vita‐Salute IRCCS Ospedale San RaffaeleMilanoItaly
- Vita‐Salute San Raffaele UniversityMilanItaly
| | - Tiziana Anelli
- Division of Genetics and Cell BiologyUniversità Vita‐Salute IRCCS Ospedale San RaffaeleMilanoItaly
- Vita‐Salute San Raffaele UniversityMilanItaly
| | - Tuan Nguyen
- Department ChemistryTechnical University MunichGarchingGermany
| | | | - Roberto Sitia
- Division of Genetics and Cell BiologyUniversità Vita‐Salute IRCCS Ospedale San RaffaeleMilanoItaly
- Vita‐Salute San Raffaele UniversityMilanItaly
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3D Structures of IgA, IgM, and Components. Int J Mol Sci 2021; 22:ijms222312776. [PMID: 34884580 PMCID: PMC8657937 DOI: 10.3390/ijms222312776] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2021] [Revised: 11/20/2021] [Accepted: 11/23/2021] [Indexed: 12/02/2022] Open
Abstract
Immunoglobulin G (IgG) is currently the most studied immunoglobin class and is frequently used in antibody therapeutics in which its beneficial effector functions are exploited. IgG is composed of two heavy chains and two light chains, forming the basic antibody monomeric unit. In contrast, immunoglobulin A (IgA) and immunoglobulin M (IgM) are usually assembled into dimers or pentamers with the contribution of joining (J)-chains, which bind to the secretory component (SC) of the polymeric Ig receptor (pIgR) and are transported to the mucosal surface. IgA and IgM play a pivotal role in various immune responses, especially in mucosal immunity. Due to their structural complexity, 3D structural study of these molecules at atomic scale has been slow. With the emergence of cryo-EM and X-ray crystallographic techniques and the growing interest in the structure-function relationships of IgA and IgM, atomic-scale structural information on IgA-Fc and IgM-Fc has been accumulating. Here, we examine the 3D structures of IgA and IgM, including the J-chain and SC. Disulfide bridging and N-glycosylation on these molecules are also summarized. With the increasing information of structure–function relationships, IgA- and IgM-based monoclonal antibodies will be an effective option in the therapeutic field.
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10
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Sopp JM, Peters SJ, Rowley TF, Oldham RJ, James S, Mockridge I, French RR, Turner A, Beers SA, Humphreys DP, Cragg MS. On-target IgG hexamerisation driven by a C-terminal IgM tail-piece fusion variant confers augmented complement activation. Commun Biol 2021; 4:1031. [PMID: 34475514 PMCID: PMC8413284 DOI: 10.1038/s42003-021-02513-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Accepted: 08/02/2021] [Indexed: 12/20/2022] Open
Abstract
The majority of depleting monoclonal antibody (mAb) drugs elicit responses via Fc-FcγR and Fc-C1q interactions. Optimal C1q interaction is achieved through hexameric Fc:Fc interactions at the target cell surface. Herein is described an approach to exploit the tailpiece of the naturally multimeric IgM to augment hexamerisation of IgG. Fusion of the C-terminal tailpiece of IgM promoted spontaneous hIgG hexamer formation, resulting in enhanced C1q recruitment and complement-dependent cytotoxicity (CDC) but with off-target complement activation and reduced in-vivo efficacy. Mutation of the penultimate tailpiece cysteine to serine (C575S) ablated spontaneous hexamer formation, but facilitated reversible hexamer formation after concentration in solution. C575S mutant tailpiece antibodies displayed increased complement activity only after target binding, in-line with the concept of 'on-target hexamerisation', whilst retaining efficient in-vivo efficacy and augmented target cell killing in the lymph node. Hence, C575S-tailpiece technology represents an alternative format for promoting on-target hexamerisation and enhanced CDC.
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Affiliation(s)
- Joshua M Sopp
- Antibody and Vaccine Group, Centre for Cancer Immunology, Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton, UK
| | | | | | - Robert J Oldham
- Antibody and Vaccine Group, Centre for Cancer Immunology, Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton, UK
| | - Sonya James
- Antibody and Vaccine Group, Centre for Cancer Immunology, Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton, UK
| | - Ian Mockridge
- Antibody and Vaccine Group, Centre for Cancer Immunology, Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton, UK
| | - Ruth R French
- Antibody and Vaccine Group, Centre for Cancer Immunology, Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton, UK
| | | | - Stephen A Beers
- Antibody and Vaccine Group, Centre for Cancer Immunology, Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton, UK
| | | | - Mark S Cragg
- Antibody and Vaccine Group, Centre for Cancer Immunology, Cancer Sciences, Faculty of Medicine, University of Southampton, Southampton, UK.
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Tempio T, Anelli T. The pivotal role of ERp44 in patrolling protein secretion. J Cell Sci 2020; 133:133/21/jcs240366. [PMID: 33173013 DOI: 10.1242/jcs.240366] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Interactions between protein ligands and receptors are the main language of intercellular communication; hence, how cells select proteins to be secreted or presented on the plasma membrane is a central concern in cell biology. A series of checkpoints are located along the secretory pathway, which ensure the fidelity of such protein signals (quality control). Proteins that pass the checkpoints operated in the endoplasmic reticulum (ER) by the binding immunoglobulin protein (BiP; also known as HSPA5 and GRP78) and the calnexin-calreticulin systems, must still overcome additional scrutiny in the ER-Golgi intermediate compartment (ERGIC) and the Golgi. One of the main players of this process in all metazoans is the ER-resident protein 44 (ERp44); by cycling between the ER and the Golgi, ERp44 controls the localization of key enzymes designed to act in the ER but that are devoid of suitable localization motifs. ERp44 also patrols the secretion of correctly assembled disulfide-linked oligomeric proteins. Here, we discuss the mechanisms driving ERp44 substrate recognition, with important consequences on the definition of 'thiol-mediated quality control'. We also describe how pH and zinc gradients regulate the functional cycle of ERp44, coupling quality control and membrane trafficking along the early secretory compartment.
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Affiliation(s)
- Tiziana Tempio
- Division of Genetics and Cell Biology, Vita-Salute San Raffaele University, Milan 20132, Italy.,IRCCS San Raffaele Scientific Institute, Milan 20132, Italy
| | - Tiziana Anelli
- Division of Genetics and Cell Biology, Vita-Salute San Raffaele University, Milan 20132, Italy .,IRCCS San Raffaele Scientific Institute, Milan 20132, Italy
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12
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Keyt BA, Baliga R, Sinclair AM, Carroll SF, Peterson MS. Structure, Function, and Therapeutic Use of IgM Antibodies. Antibodies (Basel) 2020; 9:E53. [PMID: 33066119 PMCID: PMC7709107 DOI: 10.3390/antib9040053] [Citation(s) in RCA: 95] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Accepted: 10/09/2020] [Indexed: 12/18/2022] Open
Abstract
Natural immunoglobulin M (IgM) antibodies are pentameric or hexameric macro-immunoglobulins and have been highly conserved during evolution. IgMs are initially expressed during B cell ontogeny and are the first antibodies secreted following exposure to foreign antigens. The IgM multimer has either 10 (pentamer) or 12 (hexamer) antigen binding domains consisting of paired µ heavy chains with four constant domains, each with a single variable domain, paired with a corresponding light chain. Although the antigen binding affinities of natural IgM antibodies are typically lower than IgG, their polyvalency allows for high avidity binding and efficient engagement of complement to induce complement-dependent cell lysis. The high avidity of IgM antibodies renders them particularly efficient at binding antigens present at low levels, and non-protein antigens, for example, carbohydrates or lipids present on microbial surfaces. Pentameric IgM antibodies also contain a joining (J) chain that stabilizes the pentameric structure and enables binding to several receptors. One such receptor, the polymeric immunoglobulin receptor (pIgR), is responsible for transcytosis from the vasculature to the mucosal surfaces of the lung and gastrointestinal tract. Several naturally occurring IgM antibodies have been explored as therapeutics in clinical trials, and a new class of molecules, engineered IgM antibodies with enhanced binding and/or additional functional properties are being evaluated in humans. Here, we review the considerable progress that has been made regarding the understanding of biology, structure, function, manufacturing, and therapeutic potential of IgM antibodies since their discovery more than 80 years ago.
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Affiliation(s)
- Bruce A. Keyt
- IGM Biosciences Inc, 325 East Middlefield Road, Mountain View, CA 94043, USA; (R.B.); (A.M.S.); (S.F.C.); (M.S.P.)
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13
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Kolopp-Sarda MN, Miossec P. Contribution of Hepatitis C Infection to a Large Cohort of Cryoglobulin-Positive Patients: Detection and Characteristics. Front Immunol 2020; 11:1183. [PMID: 32695098 PMCID: PMC7338377 DOI: 10.3389/fimmu.2020.01183] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Accepted: 05/13/2020] [Indexed: 01/29/2023] Open
Abstract
Cryoglobulins (CGs) are cold precipitating immunoglobulins, and hepatitis C virus (HCV) infection is its most common cause. The purpose of the study was to determine the contribution of HCV in a large cohort of CG. Biological characteristics and specificity of CGs in HCV patients were compared to non-HCV subjects. Cryoglobulin analysis included isotype, clonality, concentration, and rheumatoid factor (RF) in cryoprecipitate and serum complement and RF. This study is an extension of the study carried out on a cohort of 13,439 patients tested for CGs from all medical units, in which 1,675/13,439 (12.5%) patients had a CG, and 680/1,675 (40.6%) had HCV serology or viral load determination (HCV RNA). Among these 680 CG patients tested for HCV, 325 of 680 (47.8%) HCV patients (272 HCV RNA+ and 45 HCV RNA− patients) were compared to 355/680 (52.2%) non-HCV subjects. After a positive detection of CG, HCV status was determined only for 37.7% (256/680) of patients, allowing the diagnosis of a previously unknown HCV infection for 39.8% (102/256). Concentration of HCV RNA+ CGs (median = 80.5 mg/L) was significantly higher than that of HCV RNA− CG (median = 50.5 mg/L, p = 0.001) and HCV− CG (median = 32 mg/L, p < 0.0001). There was no difference of median CG concentration between HCV RNA− patients and non-HCV subjects. Rheumatoid factor titer was significantly higher in type II CG compared to type III CG in HCV RNA+ patients (254 ± 720 vs. 15 ± 21 IU/mL, p < 0.0001) and non-HCV subjects (333 ± 968 vs. 16.8 ± 26 IU/mL, p = 0.0004). Complement functional activity CH50 was lower in HCV RNA+ patients (36 ± 24 U/mL) and in HCV RNA− patients (32 ± 21 U/mL) than in non-HCV subjects (50 ± 25 U/mL, p = 0.001 and p = 0.004). In conclusion, HCV infection and treatment influence CG characteristics. It is essential, and far from always tested, to determine the HCV status of patients with mixed CG, and conversely to search for CG in patients with HCV infection.
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Affiliation(s)
- Marie N Kolopp-Sarda
- Immunogenomics and Inflammation Research Unit EA 4130, University of Lyon, Lyon, France.,Immunology Laboratory, Hospices Civils de Lyon, Lyon, France
| | - Pierre Miossec
- Immunogenomics and Inflammation Research Unit EA 4130, University of Lyon, Lyon, France.,Department of Immunology and Rheumatology, Clinical Immunology Unit, Hospices Civils de Lyon, Lyon, France
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14
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Li Y, Wang G, Li N, Wang Y, Zhu Q, Chu H, Wu W, Tan Y, Yu F, Su XD, Gao N, Xiao J. Structural insights into immunoglobulin M. Science 2020; 367:1014-1017. [PMID: 32029689 DOI: 10.1126/science.aaz5425] [Citation(s) in RCA: 75] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 01/24/2020] [Indexed: 12/21/2022]
Abstract
Immunoglobulin M (IgM) plays a pivotal role in both humoral and mucosal immunity. Its assembly and transport depend on the joining chain (J-chain) and the polymeric immunoglobulin receptor (pIgR), but the underlying molecular mechanisms of these processes are unclear. We report a cryo-electron microscopy structure of the Fc region of human IgM in complex with the J-chain and pIgR ectodomain. The IgM-Fc pentamer is formed asymmetrically, resembling a hexagon with a missing triangle. The tailpieces of IgM-Fc pack into an amyloid-like structure to stabilize the pentamer. The J-chain caps the tailpiece assembly and bridges the interaction between IgM-Fc and the polymeric immunoglobulin receptor, which undergoes a large conformational change to engage the IgM-J complex. These results provide a structural basis for the function of IgM.
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Affiliation(s)
- Yaxin Li
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Guopeng Wang
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China
| | - Ningning Li
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China.,State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China
| | - Yuxin Wang
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Qinyu Zhu
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Huarui Chu
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China.,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
| | - Wenjun Wu
- Renal Division, Department of Medicine, Peking University First Hospital, Beijing, China.,Institute of Nephrology, Peking University, Beijing, China
| | - Ying Tan
- Renal Division, Department of Medicine, Peking University First Hospital, Beijing, China.,Institute of Nephrology, Peking University, Beijing, China
| | - Feng Yu
- Renal Division, Department of Medicine, Peking University First Hospital, Beijing, China.,Institute of Nephrology, Peking University, Beijing, China.,Department of Nephrology, Peking University International Hospital, Beijing, China
| | - Xiao-Dong Su
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China
| | - Ning Gao
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China.,State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing, China
| | - Junyu Xiao
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, Beijing, China. .,Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, China
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15
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Weber B, Maier A, Buchner J. Peptides in proteins. J Pept Sci 2019; 26:e3235. [PMID: 31867828 DOI: 10.1002/psc.3235] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Revised: 10/28/2019] [Accepted: 11/04/2019] [Indexed: 12/18/2022]
Abstract
During evolution C-terminal peptide extensions were added to proteins on the gene level. These convey additional functions such as interaction with partner proteins or oligomerisation. IgM antibodies and molecular chaperones are two prominent examples discussed.
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Affiliation(s)
- Benedikt Weber
- Center for Integrated Protein Science Munich at the Department Chemie, Technische Universität München, Garching, Germany
| | - Andreas Maier
- Center for Integrated Protein Science Munich at the Department Chemie, Technische Universität München, Garching, Germany
| | - Johannes Buchner
- Center for Integrated Protein Science Munich at the Department Chemie, Technische Universität München, Garching, Germany
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16
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Su Y, Wang B, Zhang Y, Ruan Z, Bai H, Wan J, Xu C, Li G, Wang S, Ai H, Xiong L, Geng H. Mass spectrometric determination of disulfide bonds and free cysteine in grass carp IgM isoforms. FISH & SHELLFISH IMMUNOLOGY 2019; 95:287-296. [PMID: 31669895 DOI: 10.1016/j.fsi.2019.10.051] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Revised: 09/21/2019] [Accepted: 10/24/2019] [Indexed: 06/10/2023]
Abstract
Disulfide bonds are fundamental in establishing Ig structure and maintaining Ig biological function. Here, we analysed disulfide bonds and free cysteine in three grass carp IgM isoforms (monomeric, dimeric/trimeric, and tetrameric IgM) by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The results revealed that Cys574 residue status at the C-terminal tail differed substantially in monomeric IgM in comparison with polymeric IgM, Cys574 was found as free thiol in monomeric IgM, while it formed disulfide linkages in dimeric/trimeric and tetrameric IgM. Five intra-chain disulfide bonds in the CH1~CH4 and CL1 domains, as well as one H-H and one H-L inter-chain disulfide linkages, were also observed and shown identical connectivity in monomeric, dimeric/trimeric, and tetrameric IgM. These findings represent the first experimental assignments of disulfide linkages of grass carp IgM and reveal that grass carp IgM isoform formation is due to alternative disulfide bonds connecting the Cys574 residue at the C-terminal tail.
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Affiliation(s)
- Yiling Su
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Bing Wang
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Ying Zhang
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Zilun Ruan
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Hao Bai
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Jian Wan
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Chen Xu
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Guoqi Li
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Shengqiang Wang
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Hui Ai
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Li Xiong
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Hui Geng
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China.
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17
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MZB1 promotes the secretion of J-chain-containing dimeric IgA and is critical for the suppression of gut inflammation. Proc Natl Acad Sci U S A 2019; 116:13480-13489. [PMID: 31127044 DOI: 10.1073/pnas.1904204116] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
IgA is the most abundantly produced antibody in the body and plays a crucial role in gut homeostasis and mucosal immunity. IgA forms a dimer that covalently associates with the joining (J) chain, which is essential for IgA transport into the mucosa. Here, we demonstrate that the marginal zone B and B-1 cell-specific protein (MZB1) interacts with IgA through the α-heavy-chain tailpiece dependent on the penultimate cysteine residue and prevents the intracellular degradation of α-light-chain complexes. Moreover, MZB1 promotes J-chain binding to IgA and the secretion of dimeric IgA. MZB1-deficient mice are impaired in secreting large amounts of IgA into the gut in response to acute inflammation and develop severe colitis. Oral administration of a monoclonal IgA significantly ameliorated the colitis, accompanied by normalization of the gut microbiota composition. The present study identifies a molecular chaperone that promotes J-chain binding to IgA and reveals an important mechanism that controls the quantity, quality, and function of IgA.
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18
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Su YL, Wang B, Hu MD, Cui ZW, Wan J, Bai H, Yang Q, Cui YF, Wan CH, Xiong L, Zhang YA, Geng H. Site-Specific N-Glycan Characterization of Grass Carp Serum IgM. Front Immunol 2018; 9:2645. [PMID: 30487799 PMCID: PMC6246689 DOI: 10.3389/fimmu.2018.02645] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 10/26/2018] [Indexed: 01/22/2023] Open
Abstract
Immunoglobulin M (IgM) is the major antibody in teleost fish and plays an important role in humoral adaptive immunity. The N-linked carbohydrates presenting on IgM have been well documented in higher vertebrates, but little is known regarding site-specific N-glycan characteristics in teleost IgM. In order to characterize these site-specific N-glycans, we conducted the first study of the N-glycans of each glycosylation site of the grass carp serum IgM. Among the four glycosylation sites, the Asn-262, Asn-303, and Asn-426 residues were efficiently glycosylated, while Asn-565 at the C-terminal tailpiece was incompletely occupied. A striking decrease in the level of occupancy at the Asn-565 glycosite was observed in dimeric IgM compared to that in monomeric IgM, and no glycan occupancy of Asn-565 was observed in tetrameric IgM. Glycopeptide analysis with liquid chromatography-electrospray ionization tandem mass spectrometry revealed mainly complex-type glycans with substantial heterogeneity, with neutral; monosialyl-, disialyl- and trisialylated; and fucosyl-and non-fucosyl-oligosaccharides conjugated to grass carp serum IgM. Glycan variation at a single site was greatest at the Asn-262 glycosite. Unlike IgMs in other species, only traces of complex-type and no high-mannose glycans were found at the Asn-565 glycosite. Matrix-assisted laser desorption ionization analysis of released glycans confirmed the overwhelming majority of carbohydrates were of the complex-type. These results indicate that grass carp serum IgM exhibits unique N-glycan features and highly processed oligosaccharides attached to individual glycosites.
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Affiliation(s)
- Yi-Ling Su
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, China
| | - Bing Wang
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, China
| | - Meng-Die Hu
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, China
| | - Zheng-Wei Cui
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.,College of Modern Agriculture Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Jian Wan
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, China
| | - Hao Bai
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, China
| | - Qian Yang
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, China
| | - Yan-Fang Cui
- Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, Central China Normal University, Wuhan, China
| | - Cui-Hong Wan
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, China
| | - Li Xiong
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, China
| | - Yong-An Zhang
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.,State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, China.,Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China
| | - Hui Geng
- Hubei Key Laboratory of Genetic Regulation and Integrative Biology, School of Life Sciences, Central China Normal University, Wuhan, China
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19
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Hiramoto E, Tsutsumi A, Suzuki R, Matsuoka S, Arai S, Kikkawa M, Miyazaki T. The IgM pentamer is an asymmetric pentagon with an open groove that binds the AIM protein. SCIENCE ADVANCES 2018; 4:eaau1199. [PMID: 30324136 PMCID: PMC6179379 DOI: 10.1126/sciadv.aau1199] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Accepted: 08/31/2018] [Indexed: 05/09/2023]
Abstract
Soluble immunoglobulin M (IgM) forms a pentamer containing a joining (J) chain polypeptide. While IgM pentamer has various immune functions, it also behaves as a carrier of circulating apoptosis inhibitor of macrophage (AIM; also called CD5L) protein that facilitates repair during different diseases. AIM binds to the IgM pentamer solely in the presence of the J chain. Here, using a single-particle negative-stain electron microscopy, we found that the IgM pentamer exhibits an asymmetric pentagon containing one large gap, which is markedly different from the textbook symmetric pentagon model. A single AIM molecule specifically fits into the gap, cross-bridging two IgM-Fc that form the edges of the gap through a disulfide bond at one side and a charge-based interaction at the other side. The discovery of the bona fide shape of the IgM pentamer advances our structural understanding of the pentameric IgM and its binding mode with AIM.
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Affiliation(s)
- Emiri Hiramoto
- Laboratory of Molecular Biomedicine for Pathogenesis, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
| | - Akihisa Tsutsumi
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
| | - Risa Suzuki
- Laboratory of Molecular Biomedicine for Pathogenesis, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
| | - Shigeru Matsuoka
- Laboratory of Molecular Biomedicine for Pathogenesis, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
- Corresponding author. (T.M.); (S.A.)
| | - Satoko Arai
- Laboratory of Molecular Biomedicine for Pathogenesis, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
- Corresponding author. (T.M.); (S.A.)
| | - Masahide Kikkawa
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
| | - Toru Miyazaki
- Laboratory of Molecular Biomedicine for Pathogenesis, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
- AMED-CREST, Japan Agency for Medical Research and Development, Tokyo, Japan
- Max Planck–The University of Tokyo Center for Integrative Inflammology, Tokyo, Japan
- Corresponding author. (T.M.); (S.A.)
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