Implications of the Near-Planar Solution Structure of Human Myeloma Dimeric IgA1 for Mucosal Immunity and IgA Nephropathy This information is current as Alexandra Bonner, Patricia B. Furtado, Adel Almogren, of September 26, 2021. Michael A. Kerr and Stephen J. Perkins J Immunol 2008; 180:1008-1018; ; doi: 10.4049/jimmunol.180.2.1008 http://www.jimmunol.org/content/180/2/1008 Downloaded from References This article cites 35 articles, 12 of which you can access for free at: http://www.jimmunol.org/content/180/2/1008.full#ref-list-1 http://www.jimmunol.org/ Why The JI? Submit online. • Rapid Reviews! 30 days* from submission to initial decision • No Triage! Every submission reviewed by practicing scientists • Fast Publication! 4 weeks from acceptance to publication by guest on September 26, 2021 *average Subscription Information about subscribing to The Journal of Immunology is online at: http://jimmunol.org/subscription Permissions Submit copyright permission requests at: http://www.aai.org/About/Publications/JI/copyright.html Email Alerts Receive free email-alerts when new articles cite this article. Sign up at: http://jimmunol.org/alerts The Journal of Immunology is published twice each month by The American Association of Immunologists, Inc., 1451 Rockville Pike, Suite 650, Rockville, MD 20852 Copyright © 2008 by The American Association of Immunologists All rights reserved. Print ISSN: 0022-1767 Online ISSN: 1550-6606. The Journal of Immunology Implications of the Near-Planar Solution Structure of Human Myeloma Dimeric IgA1 for Mucosal Immunity and IgA Nephropathy1 Alexandra Bonner,* Patricia B. Furtado,* Adel Almogren,† Michael A. Kerr,‡ and Stephen J. Perkins2* IgA is unique in being able to form a diverse range of polymeric structures. Increases in the levels of dimeric IgA1 (dIgA1) in serum have been implicated in diseases such as IgA nephropathy. We have determined the solution structure for dIgA1 by synchrotron x-ray and neutron scattering and analytical ultracentrifugation. The Guinier radius of gyration (RG) of 7.60–8.65 nm indicated that the two monomers within dIgA1 are arranged in an extended conformation. The distance distribution curve P(r) gave an overall length (L) of 22–26 nm. These results were confirmed by the sedimentation coefficient and frictional ratio of dIgA1. Downloaded from Constrained scattering modeling starting from the IgA1 monomer solution structure revealed a near-planar dimer structure for dIgA1. The two Fc regions form a slightly bent arrangement in which they form end-to-end contacts, and the J chain was located at this interface. This structure was refined by optimizing the position of the four Fab regions. From this, the best-fit solution structures show that the four Fab Ag-binding sites are independent of one another, and the two Fc regions are accessible to receptor binding. This arrangement allows dIgA1 to initiate specific immune responses by binding to Fc␣RI receptors, while still retaining Ag-binding ability, and to be selectively transported to mucosal surfaces by binding to the polymeric Ig receptor to form http://www.jimmunol.org/ secretory IgA. A mechanism for the involvement of dIgA1 oligomers in the pathology of IgA nephropathy is discussed in the light of this near-planar structure. The Journal of Immunology, 2008, 180: 1008–1018. mmunoglobulin A is the most abundant Ab class found in (SIgA). Transport of dIgA across the epithelium into luminal se- mucosal surfaces and is also the most heterogeneous human cretions, and the consequent formation of SIgA is facilitated by the I Ab class, being present in two subclasses IgA1 and IgA2 of polymeric Ig receptor (pIgR). dIgA binds to pIgR at the basolateral which there are at least two different allotypes. This is reflected in surface of the epithelial cell, whereupon it is transcytosed across the diverse functional properties of IgA, which are still not fully the cell and released into the lumen following cleavage of pIgR at by guest on September 26, 2021 understood (1). Unlike any other Ig class, IgA occurs in different the apical membrane. SIgA is released, with the extracellular pIgR oliogomeric states, circulating in serum predominantly as mono- domains (now called SC) remaining bound to the IgA dimer. The meric IgA at 3 mg/ml, and at mucosal surfaces as polymeric IgA, solution structure of SC has recently been elucidated (4). mainly as dimeric IgA covalently linked with secretory component An increased IgA level in serum can be associated with IgA 3 (SC) (2). In serum, IgA is the second most abundant Ab class, nephropathy (IgAN) which is the most common form of chronic ϳ with 90% being IgA1. Monomeric and dimeric IgA (dIgA) in- glomerulonephritis worldwide. IgAN is a renal disease involving ␣ ␣ teract with the cell surface Fc R (Fc RI; CD89) to perform im- the inflammation of the glomeruli in the kidneys, and is charac- mune functions including the linking of the humoral and cellular terized by the mesangial deposition of polymeric IgA1. IgAN is immune response (3). In mucosal linings, lymphoid cells produce caused by either an abnormality in IgA1 itself or in the production dIgA locally, which is secreted into the mucosa as secretory IgA of IgA1, rather than an intrinsic abnormality in the glomerulus (5). Some reported characteristics of IgA in IgAN include abnormal *Department of Biochemistry and Molecular Biology, University College London, O-glycosylation and an increased ␭/␬ L chain ratio (6). Serum † London, United Kingdom; Department of Pathology, College of Medicine and King from IgA myeloma patients can be rich in dIgA1 and polymeric Khalid University Hospital, King Saud University, Riyadh, Saudi Arabia; and ‡De- partment of Clinical Biochemistry and Immunology, General Infirmary, Leeds, IgA, although this does not lead to IgAN. In IgA myeloma and in United Kingdom other diseases characterized by high levels of dIgA1 and polymeric Received for publication September 17, 2007. Accepted for publication November IgA, these forms of IgA are thought to play an important role in 9, 2007. some of the pathology associated with these diseases (7). The costs of publication of this article were defrayed in part by the payment of page Polymeric IgA consists of two (or sometimes three or four) IgA charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. monomers bound covalently through a joining chain (J chain) (Fig. 1 This work was supported by the Biotechnology and Biological Sciences Research 1). Monomeric IgA has a 12-domain structure arranged as two H Council. and two L chains (Fig. 1). Crystal structures are known for the 2 Address correspondence and reprint requests to Dr. Stephen J. Perkins, Department murine Fab region of IgA and the human Fc region of IgA1 bound of Biochemistry and Molecular Biology, Darwin Building, University College ␣ London, Gower Street, London WC1E 6BT, U.K. E-mail address: s.perkins@ to Fc RI (8, 9). The topology of each of the IgA domains is a medsch.ucl.ac.uk ␤-sheet sandwich comprised of the DEBA and GFC ␤-strands for 3 Abbreviations used in this paper: SC, secretory component; dIgA1, dimeric IgA1; the seven-stranded C-type domains and the DEBA and GFCCЈCЉ SIgA, secretory IgA; pIgR, polymeric Ig receptor; IgAN, IgA nephropathy; HSA, ␤-strands for the nine-stranded V-type domain (10). IgA1 and human serum albumin. IgA2 differ significantly in the hinge region where IgA2 lacks a Copyright © 2008 by The American Association of Immunologists, Inc. 0022-1767/08/$2.00 Pro-, Ser-, and Thr-rich sequence of 13 aa that is present in IgA1 www.jimmunol.org The Journal of Immunology 1009 the formation of SIgA. Insight is also provided into the role of dIgA1 in the development of IgAN. Materials and Methods Preparation and composition of dIgA1 A monoclonal dIgA1 with ␬-class L chain was isolated from a human myeloma serum using a combination of thiophilic chromatography and jacalin-agarose lectin affinity chromatography (24, 25). Samples were sub- jected to size-exclusion chromatography to remove nonspecific aggregates and checked by reducing and nonreducing SDS-PAGE to confirm sample integrities before and after data collection. For x-ray scattering and ana- lytical ultracentrifugation experiments, dIgA1 was dialyzed into Dulbecco’s PBS supplemented with EDTA and sodium azide as antibacterial preser- vatives (12.5 mM sodium phosphate, 140 mM NaCl, 0.5 mM EDTA, 0.02% NaN3, pH 7.4). For neutron scattering, the buffer was Dulbecco’s 2 PBS as above, dialyzed at 6°C into 100% H2O for 36 h with four buffer changes. The dIgA1 amino acid and carbohydrate composition for data analyses corresponds to two IgA1 molecules as previously described (16). The human J chain sequence was taken from the SWISSPROT sequence code P01591, to which another biantennary complex-type oligosaccharide Downloaded from 49 FIGURE 1. The domain structure and sequence of dIgA1. dIgA1 is was added at Asn . This resulted in the following: molecular mass, 344.8 3 3 formed by two IgA1 monomers that are covalently linked with the J chain. kDa, an unhydrated volume of 439.4 nm , a hydrated volume of 580.2 nm , Each IgA1 H chain contains the V ,C 1, C 2, and C 3 domains, and each an absorption coefficient at 280 nm of 12.3 (1%, 1 cm), and a partial H H H H specific volume v៮ of 0.724 ml/g. L chain contains the VL and CL domains. The V and C domains are high- lighted with gray and white backgrounds, respectively. The CDRs (black crescents), the 23-residue hinge peptide (dashed line), and the 18-residue X-ray and neutron scattering C-terminal tailpiece (dashed line) are highlighted. Inter-H chain disulphide http://www.jimmunol.org/ bridges at Cys241-Cys241 and two at Cys242-Cys299 are shown as three black Solution scattering is a diffraction technique that studies the overall struc- ture of biological macromolecules in random orientations in solution (23).