Crystal structure at 2.2 Å resolution of the MHC-related neonatal Fc receptor

Burmeister, W.P.; Gastinel, Louis N.; Simister, Neil E.; Blum, Michael L.; Björkman, Pamela J.

doi:10.1038/372336a0

Cited by 306 publications

(219 citation statements)

References 45 publications

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“…The enlarged gold particles were in locations suggesting they represented enhanced 1.4 nm Nanogold attached to Fc that was bound to FcRn: near the inner membrane leaflets of tubular vesicles (Figure 4a and 5) and multivesicular bodies (Figure 4b), and in the extracellular space near the basolateral surface (Figure 4c, 5d). Notably, the majority of enhanced Au-Fc particles in duodenal samples were found within a 6-7 nm distance from a membrane, implying attachment to FcRn, which has an ∼5 nm ectodomain (Burmeister et al, 1994). In the ileum, we again saw enhanced gold particles inside degradative vesicles (Figure 4d), consistent with fluid phase uptake in this region of the neonatal intestine.…”

Section: A New Methods To Enlarge 14 Nm Gold Clusters In Hpf/fsf Samplessupporting

confidence: 65%

A freeze substitution fixation-based gold enlarging technique for EM studies of endocytosed Nanogold-labeled molecules

Kivork

Machinani

et al. 2007

Journal of Structural Biology

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We have developed methods to locate individual ligands that can be used for electron microscopy studies of dynamic events during endocytosis and subsequent intracellular trafficking. The methods are based on enlargement of 1.4 nm Nanogold attached to an endocytosed ligand. Nanogold, a small label that does not induce misdirection of ligand-receptor complexes, is ideal for labeling ligands endocytosed by live cells, but is too small to be routinely located in cells by electron microscopy. Traditional pre-embedding enhancement protocols to enlarge Nanogold are not compatible with high pressure freezing/freeze substitution fixation (HPF/FSF), the most accurate method to preserve ultrastructure and dynamic events during trafficking. We have developed an improved enhancement procedure for chemically-fixed samples that reduced autonucleation, and a new pre-embedding goldenlarging technique for HPF/FSF samples that preserved contrast and ultrastructure and can be used for high-resolution tomography. We evaluated our methods using labeled Fc as a ligand for the neonatal Fc receptor. Attachment of Nanogold to Fc did not interfere with receptor binding or uptake, and gold-labeled Fc could be specifically enlarged to allow identification in 2D projections and in tomograms. These methods should be broadly applicable to many endocytosis and transcytosis studies.

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Section: A New Methods To Enlarge 14 Nm Gold Clusters In Hpf/fsf Samplessupporting

confidence: 65%

A freeze substitution fixation-based gold enlarging technique for EM studies of endocytosed Nanogold-labeled molecules

Kivork

Machinani

et al. 2007

Journal of Structural Biology

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“…The stoichiometry of the interaction between FcRn and its ligand has been a matter of debate (20, 26 -29). In the cocrystals, a long, repeating oligomeric ribbon with a 2n:n stoichiometry was observed, in which FcRn dimers are bridged by Fc molecules so that every Fc dimer interacts with two receptors (38). Studies also suggested that the 2:1 FcRn-Fc complex is formed in solution, although FcRn is not capable of dimerization in these conditions (28,29).…”

Section: Discussionmentioning

confidence: 93%

“…In one binding mechanism, the two FcRn molecules bind symmetrically to two Fc monomers in a dimeric Fc, and in the other, the two FcRn bind asymmetrically: the first FcRn molecule binds to an Fc monomer in a similar manner to the FcRn-mFc binding, and the binding of the second FcRn to Fc must have a low affinity, to give an overall comparable K D to the one-step FcRn-mFc binding. The latter mechanism seems more likely because a bent, asymmetrical Fc structure was found in the 1:1 FcRn/hdFc (heterodimeric Fc that can only bind one FcRn) cocrystal (38). The low affinity of the second FcRn binding is probably due to the conformational change in Fc caused by the binding of the first FcRn.…”

Section: Discussionmentioning

confidence: 99%

Soluble Monomeric IgG1 Fc

Ying

Chen

Gong

et al. 2012

Journal of Biological Chemistry

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“…As with all members of the family, a prominent feature of the ␣ 1 and ␣ 2 domains is a pair of opposing ␣-helices that enclose the binding groove for peptides or (glyco)lipids in MHC proteins. In FcRn, HFE, and MIC-A, the groove is closed, and there is no evidence for ligand binding within the region between the helices, although each interacts with other proteins (15)(16)(17). In ZAG, however, the x-ray crystal structure shows that the groove is open and contains an additional electron density ascribed to an unidentified ligand ( Fig.…”

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confidence: 99%

Hydrophobic Ligand Binding by Zn-α2-glycoprotein, a Soluble Fat-depleting Factor Related to Major Histocompatibility Complex Proteins

Kennedy¹,

Heikema²,

Cooper³

et al. 2001

Journal of Biological Chemistry

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Zn-␣ 2 -glycoprotein (ZAG) is a member of the major histocompatibility complex (MHC) class I family of proteins and is identical in amino acid sequence to a tumorderived lipid-mobilizing factor associated with cachexia in cancer patients. ZAG is present in plasma and other body fluids, and its natural function, like leptin's, probably lies in lipid store homeostasis. X-ray crystallography has revealed an open groove between the helices of ZAG's ␣ 1 and ␣ 2 domains, containing an unidentified small ligand in a position similar to that of peptides in MHC proteins (Sanchez, L. M., Chirino, A. J., and Bjorkman, P. J. (1999) Science 283, 1914 -1919). Here we show, using serum-derived and bacterial recombinant protein, that ZAG binds the fluorophore-tagged fatty acid 11-(dansylamino)undecanoic acid (DAUDA) and, by competition, natural fatty acids such as arachidonic, linolenic, eicosapentaenoic, and docosahexaenoic acids. Other MHC class I-related proteins (FcRn, HFE, HLA-Cw*0702) showed no such evidence of binding. Fluorescence and isothermal calorimetry analysis showed that ZAG binds DAUDA with K d in the micromolar range, and differential scanning calorimetry showed that ligand binding increases the thermal stability of the protein. Addition of fatty acids to ZAG alters its intrinsic (tryptophan) fluorescence emission spectrum, providing a strong indication that ligand binds in the expected position close to a cluster of exposed tryptophan side chains in the groove. This study therefore shows that ZAG binds small hydrophobic ligands, that the natural ligand may be a polyunsaturated fatty acid, and provides a fluorescencebased method for investigating ZAG-ligand interactions. Zn-␣ 2 -glycoprotein (ZAG)1 is a soluble protein present in serum and other body fluids (1, 2). It accumulates in breast cysts, is produced by 40% of breast carcinomas, and is inducible in breast cancer cell lines by glucocorticoids and androgens (2,3). ZAG is identical in amino acid sequence to lipid-mobilizing factor that is associated with cachexia (4, 5), the wasting syndrome involving depletion of adipose and muscle tissue, such as occurs in many patients with cancer, AIDS, trypanosomiasis, and other life-threatening diseases. Significantly, ZAG is overexpressed in tumors that accompany fat loss, and exogenous ZAG produces cachectic symptoms in experimental animals (4, 5). ZAG, like leptin (6), therefore, participates in lipid store homeostasis, the dysregulation of which has serious implications for survival and the management of cancer and other diseases. ZAG is a member of a family of proteins typified by the class I MHC proteins (which present peptides to cytotoxic T cells) (7) and includes CD1 (which presents lipidic antigens to T cells) (8, 9), the neonatal Fc receptor (FcRn; involved in transportation of immunoglobulin across epithelia), and HFE (a transferrinbinding protein that regulates iron homeostasis) (10,11). In contrast to all other MHC-like proteins, ZAG and MIC-A (a divergent member of the MHC family) are not found in asso...

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Crystal structure at 2.2 Å resolution of the MHC-related neonatal Fc receptor

Cited by 306 publications

References 45 publications

A freeze substitution fixation-based gold enlarging technique for EM studies of endocytosed Nanogold-labeled molecules

A freeze substitution fixation-based gold enlarging technique for EM studies of endocytosed Nanogold-labeled molecules

Soluble Monomeric IgG1 Fc

Hydrophobic Ligand Binding by Zn-α2-glycoprotein, a Soluble Fat-depleting Factor Related to Major Histocompatibility Complex Proteins

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