Interplay of J chain and disulfide bonding in assembly of polymeric IgM

Fazel, Shafie; Wiersma, Erik J.; Shulman, Marc J.

doi:10.1093/intimm/9.8.1149

Cited by 23 publications

(19 citation statements)

References 48 publications

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“…J chain has been shown to be necessary for the assembly of IgA dimers (20,21). We now show that in the presence of ␣tp, the requirements for J chain incorporation closely resemble the requirements for specific dimer formation, namely the presence C ␣ 3.…”

Section: Discussionmentioning

confidence: 53%

Structural Requirements for Polymeric Immunoglobulin Assembly and Association with J Chain

Yoo¹,

Coloma

Trinh

et al. 1999

Journal of Biological Chemistry

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Both IgM and IgA exist as polymeric immunoglobulins. IgM is assembled into pentamers with J chain and hexamers lacking J chain. In contrast, polymeric IgA exists mostly as dimers with J chain. Both IgM and IgA possess an 18-amino acid extension of the C terminus (the tail-piece (tp)) that participates in polymerization through a penultimate cysteine residue. The IgM (tp) and IgA (␣tp) tail-pieces differ at seven amino acid positions. However, the tail-pieces by themselves do not determine the extent of polymerization. We now show that the restriction of polymerization to dimers requires both C ␣ 3 and ␣tp and that more efficient dimer assembly occurs when C ␣ 2 is also present; the dimers contain J chain. Formation of pentamers containing J chain requires C 3, C 4, and the tp. IgM-␣tp is present mainly as hexamers lacking J chain, and ␥-tp forms tetramers and hexamers lacking J chain, whereas IgA-tp is present as high order polymers containing J chain. In addition, there is heterogeneous processing of the Nlinked carbohydrate on IgA-tp, with some remaining in the high mannose state. These data suggest that in addition to the tail-piece, structural motifs in the constant region domains are critical for polymer assembly and J chain incorporation.

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Section: Discussionmentioning

confidence: 53%

Structural Requirements for Polymeric Immunoglobulin Assembly and Association with J Chain

Yoo¹,

Coloma

Trinh

et al. 1999

Journal of Biological Chemistry

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“…IgM monomers in the pentamer are known to interact via both their C-terminal tail region and residues within the C 3 domain, including Cys-291 (23,24). The small J chain interacts with the C-terminal tail (23,24) and could play a role in the assembly of the pentamer (24).…”

Section: Resultsmentioning

confidence: 99%

“…The small J chain interacts with the C-terminal tail (23,24) and could play a role in the assembly of the pentamer (24). This chain, however, is not expected to have a significant impact on the local structure of the monomers around the Cys-291 residues, and so it was not included in this modeling.…”

Section: Resultsmentioning

confidence: 99%

The human IgM pentamer is a mushroom-shaped molecule with a flexural bias

Czajkowsky

Shao

2009

Proc. Natl. Acad. Sci. U.S.A.

178

146

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The textbook planar model of pentameric IgM, a potent activator of complement C1q, is based upon the crystallographic structure of IgG. Although widely accepted, key predictions of this model have not yet been directly confirmed, which is particularly important since IgG lacks a major Ig fold domain in its Fc region that is present in IgM. Here, we construct a homology-based structural model of the IgM pentamer using the recently obtained crystallographic structure of IgE Fc, which has this additional Ig domain, under the constraint that all of the cysteine residues known to form disulfide bridges both within each monomer and between monomers are bonded together. In contrast to the planar model, this model predicts a non-planar, mushroom-shaped complex, with the central portion formed by the C-terminal domains protruding out of the plane formed by the Fab domains. This unexpected conformation of IgM is, however, directly confirmed by cryo-atomic force microscopy of individual human IgM molecules. Further analysis of this model with free energy calculations of out-of-plane Fab domain rotations reveals a pronounced asymmetry favoring flexions toward the central protrusion. This bias, together with polyvalent attachment to cell surface antigen, would ensure that the IgM pentamer is oriented on the cell membrane with its C1q binding sites fully exposed to the solution, and thus provides a mechanistic explanation for the first steps of C1q activation by IgM.AFM ͉ homology modeling ͉ immunoglobulin ͉ single molecule P entameric IgM is an important component of the first line of defense against foreign pathogens (1, 2) and possibly modified self-components (3), and is increasingly being developed in the diagnosis and therapy of malignancies (4-7). It is also implicated in the damage to organs and tissues following ischemia/reperfusion (8) and in multiple autoimmune diseases (9-11). Its best understood mechanism of action in the immune response is as the initiating component in the classical complement pathway mediated by C1q (12). In this, the binding of IgM to cell surface antigen enables C1q to bind to IgM, which thereby activates C1q for interactions with downstream components. The expected structural changes consequent to antigen-binding and associated with C1q activation, and how these might be modified in disease-conditions, have spurred a longstanding interest in the structure of this large multicomponent molecule (13-17).Like other antibodies, IgM monomers consist of two light and two heavy chains. However, whereas the heavy chains of most antibodies (such as IgG) contain three constant Ig domains, the heavy chains of IgM have a fourth one, as do the heavy chains in IgE. These extra (C 2) domains are located in place of the proline-rich hinge region that is responsible for the rotational flexibility of the antigen-binding Fab domains (relative to the Fc domain).Five IgM monomers complex with an additional small polypeptide (the J chain) to form the predominant oligomeric species in the human plasma (3). Obtaini...

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“…Besides the presence of additional densities on the surface of the virus, the most striking difference observed in D1D2-IgP- (25), with permission. Each long white bar represents a C2-C3 portion of the polypeptide chain, two of which form an arm.…”

Section: Resultsmentioning

confidence: 99%

Cryoelectron Tomographic Analysis of an HIV-neutralizing Protein and Its Complex with Native Viral gp120

Bennett

Ryk

et al. 2007

Journal of Biological Chemistry

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Identifying structural determinants of human immunodeficiency virus (HIV) neutralization is an important component of rational drug and vaccine design. We used cryoelectron tomography and atomic force microscopy to characterize the structure of an extremely potent HIV-neutralizing protein, D1D2-Ig␣tp (abbreviated as D1D2-IgP), a polyvalent antibody construct that presents dodecameric CD4 in place of the Fab regions. We show that D1D2-IgP has a novel structure, displaying greater flexibility of its antibody arms than the closely related IgM. Using simian immunodeficiency virus in complex with D1D2-IgP, we present unequivocal evidence that D1D2-IgP can cross-link surface spikes on the same virus and on neighboring viruses. The observed binding to the viral envelope spikes is the result of specific CD4-gp120 interaction, because binding was not observed with MICA-IgP, a construct that is identical to D1D2-IgP except that major histocompatibility complex Class I-related Chain A (MICA) replaces the CD4 moiety. CD4-mediated binding was also associated with a significantly elevated proportion of ruptured viruses. The ratio of inactivated to CD4-liganded gp120-gp41 spikes can be much greater than 1:1, because all gp120-gp41 spikes on the closely apposed surfaces of cross-linked viruses should be incapable of accessing the target cell surface and mediating entry, as a result of inter-virus spike cross-linking. These results implicate flexibility rather than steric bulk or polyvalence per se as a structural explanation for the extreme potency of D1D2-IgP and thus suggest polyvalence presented on a flexible scaffold as a key design criterion for small molecule HIV entry inhibitors. Human immunodeficiency virus type 1 (HIV-1)3 infection of target cells is initiated by binding of the viral envelope glycoprotein gp120 to the cell surface receptor CD4 (1-3). The first step in the infection process, gp120-CD4 binding is an attractive drug target because the CD4 binding site of gp120 is well conserved and because de novo infection of target cells would be blocked, preventing all subsequent stages of the viral life cycle. No therapeutic agents that target gp120-CD4 binding are currently available, although certain small molecules are in clinical trials (reviewed in Ref. 4).Soluble monomeric CD4 (sCD4) neutralizes primary isolates poorly at pharmacologically realizable concentrations (5) and is therefore not useful as a therapeutic agent against HIV-1. Minimally passaged clinical primary isolates, which best model the in vivo virus, are unaffected by physiologically sustainable concentrations of sCD4 in infectivity assays (6). Recent reports suggest that the sCD4-induced conformational fixation in gp120 (7-9) makes sCD4 binding energetically unfavorable (6).In contrast to the soluble monomeric form, CD4 on the cell surface is thought to be clustered (10, 11). The clustered CD4 may mediate an avidity effect, so that soluble CD4 competes poorly with target cell CD4 for viral gp120 (6). To mimic the clustering of cell surface CD4, Ar...

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Interplay of J chain and disulfide bonding in assembly of polymeric IgM

Cited by 23 publications

References 48 publications

Structural Requirements for Polymeric Immunoglobulin Assembly and Association with J Chain

Structural Requirements for Polymeric Immunoglobulin Assembly and Association with J Chain

The human IgM pentamer is a mushroom-shaped molecule with a flexural bias

Cryoelectron Tomographic Analysis of an HIV-neutralizing Protein and Its Complex with Native Viral gp120

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