High-resolution structures of the IgM Fc domains reveal principles of its hexamer formation

Müller, Roger; Gräwert, Melissa Ann; Kern, Thomas; Madl, Tobias; Peschek, Jirka; Sattler, Michael; Groll, M.; Büchner, Johannes

doi:10.1073/pnas.1300547110

Cited by 77 publications

(78 citation statements)

References 39 publications

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“…Even though IgNAR is known to be a covalent dimer (9), to date it has been unclear which of the IgNAR domains contribute to dimerization of the antibody molecule and how they interact. This cannot be easily deduced from the sequence, and different modes of dimerization are realized, for example, for IgM antibody domains (24). For IgNAR, we find that the isolated C1 and C3 domains each form a dimer, both in the crystal structure ( Fig.…”

Section: A Structural Analysis Of the Complete Ignar Molecule Revealsmentioning

confidence: 85%

The structural analysis of shark IgNAR antibodies reveals evolutionary principles of immunoglobulins

Feige

Gräwert

Marcinowski

et al. 2014

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

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Sharks and other cartilaginous fish are the phylogenetically oldest living organisms that rely on antibodies as part of their adaptive immune system. They produce the immunoglobulin new antigen receptor (IgNAR), a homodimeric heavy chain-only antibody, as a major part of their humoral adaptive immune response. Here, we report the atomic resolution structure of the IgNAR constant domains and a structural model of this heavy chain-only antibody. We find that despite low sequence conservation, the basic Ig fold of modern antibodies is already present in the evolutionary ancient shark IgNAR domains, highlighting key structural determinants of the ubiquitous Ig fold. In contrast, structural differences between human and shark antibody domains explain the high stability of several IgNAR domains and allowed us to engineer human antibodies for increased stability and secretion efficiency. We identified two constant domains, C1 and C3, that act as dimerization modules within IgNAR. Together with the individual domain structures and small-angle X-ray scattering, this allowed us to develop a structural model of the complete IgNAR molecule. Its constant region exhibits an elongated shape with flexibility and a characteristic kink in the middle. Despite the lack of a canonical hinge region, the variable domains are spaced appropriately wide for binding to multiple antigens. Thus, the shark IgNAR domains already display the well-known Ig fold, but apart from that, this heavy chain-only antibody employs unique ways for dimerization and positioning of functional modules. protein evolution | antibody structure | protein folding | protein engineering

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Section: A Structural Analysis Of the Complete Ignar Molecule Revealsmentioning

confidence: 85%

The structural analysis of shark IgNAR antibodies reveals evolutionary principles of immunoglobulins

Feige

Gräwert

Marcinowski

et al. 2014

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

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“…Second, does anti-VSG IgM still enter the enlarged FP of TbMORN1-depleted cells? IgM has a mass of roughly 970 kDa and a hydrodynamic radius of around 130 Å but is still efficiently internalized (48)(49)(50). Third, is the neck channel still open following TbMORN1 depletion, or has it collapsed?…”

Section: Discussionmentioning

confidence: 99%

A MORN Repeat Protein Facilitates Protein Entry into the Flagellar Pocket of Trypanosoma brucei

Morriswood

Schmidt

2015

Eukaryot Cell

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The parasite Trypanosoma brucei lives in the bloodstream of infected mammalian hosts, fully exposed to the adaptive immune system. It relies on a very high rate of endocytosis to clear bound antibodies from its cell surface. All endo-and exocytosis occurs at a single site on its plasma membrane, an intracellular invagination termed the flagellar pocket. Coiled around the neck of the flagellar pocket is a multiprotein complex containing the repeat motif protein T. brucei MORN1 (TbMORN1). In this study, the phenotypic effects of TbMORN1 depletion in the mammalian-infective form of T. brucei were analyzed. Depletion of TbMORN1 resulted in a rapid enlargement of the flagellar pocket. Dextran, a polysaccharide marker for fluid phase endocytosis, accumulated inside the enlarged flagellar pocket. Unexpectedly, however, the proteins concanavalin A and bovine serum albumin did not do so, and concanavalin A was instead found to concentrate outside it. This suggests that TbMORN1 may have a role in facilitating the entry of proteins into the flagellar pocket.T rypanosoma brucei is an important parasite of humans and domestic animals in sub-Saharan Africa, as the causative agent of sleeping sickness and nagana, respectively. Its complex life cycle involves transitions between tsetse fly vectors (its definitive hosts) and mammalian intermediate hosts. This life cycle involves a number of different cell stages, of which the procyclic form (found in the tsetse fly) and the slender bloodstream form (BSF) (found in the mammalian bloodstream) are the best studied in a laboratory setting. The procyclic form and the BSF of T. brucei share similar cytoskeletal architectures (1, 2).The principal feature of this cytoskeleton is a corset of microtubules that lie directly underneath the plasma membrane and impart to the cell its distinctive shape (3). A single invagination of the plasma membrane, termed the flagellar pocket (FP), constitutes a distinct subdomain and is found at the posterior end of the cell (4). The FP is the site of all endo-and exocytic traffic (5, 6). Abutting the FP membrane is a basal body that nucleates the single flagellum of the trypanosome cell. The flagellum exits the FP and is adhered longitudinally to the cell body along a left-handed helical path (7). Once outside the FP, the axoneme of the flagellum is paralleled by an associated intraflagellar structure called the paraflagellar rod (PFR). The PFR is composed of a paracrystalline lattice and is associated with cellular motility (8). Nucleated adjacent to the basal body is a specialized microtubule quartet that traces around the FP and then underlies the flagellum as far as the anterior end of the cell (4).The small cylinder of membrane that connects the FP to the rest of the plasma membrane constitutes a third subdomain and is called the flagellar pocket neck (FPN) (4). A number of discrete cytoskeletal structures cluster around the FPN membrane on its cytoplasmic face. Of these, the best characterized is an electrondense horseshoe-shaped structure named th...

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“…Typically, FLN-type Ig domains interact with each other via the edges of the ␤ sheets and via loop regions (10,15,22). On the other hand, many other Ig domains form dimers by interacting perpendicularly face-to-face along their ␤ sheets (62)(63)(64). In the current structures, the domains stack on each other and interact face-to-back so that their ␤ sheets are approximately parallel.…”

Section: Discussionmentioning

confidence: 99%

A Novel Structural Unit in the N-terminal Region of Filamins

Sethi

Seppälä

Tossavainen

et al. 2014

Journal of Biological Chemistry

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High-resolution structures of the IgM Fc domains reveal principles of its hexamer formation

Cited by 77 publications

References 39 publications

The structural analysis of shark IgNAR antibodies reveals evolutionary principles of immunoglobulins

The structural analysis of shark IgNAR antibodies reveals evolutionary principles of immunoglobulins

A MORN Repeat Protein Facilitates Protein Entry into the Flagellar Pocket of Trypanosoma brucei

A Novel Structural Unit in the N-terminal Region of Filamins

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