The Intrinsic Factor-Vitamin B12 Receptor and Target of Teratogenic Antibodies Is a Megalin-binding Peripheral Membrane Protein with Homology to Developmental Proteins

Moestrup, Søren K.; Kozyraki, Renata; Kristiansen, Mette Svart; Kaysen, James H.; Rasmussen, Hanne H.; Brault, D.; Pontillon, F.; Goda, F. O.; Christensen, Erik I.; Hammond, Timothy G.; Verroust, P

doi:10.1074/jbc.273.9.5235

Cited by 238 publications

(230 citation statements)

References 44 publications

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“…CUB is a large multidomain protein (460 kDa), which contains 27 tandem CUB domains that harbor the IF-Cbl-binding site (34,35). It has been proposed that a site on IF for binding the CUB receptor might lie within the segment between residues 25 and 62 (29).…”

Section: Discussionmentioning

confidence: 99%

Crystal structure of human intrinsic factor: Cobalamin complex at 2.6-Å resolution

Mathews¹,

Gordon

Chen³

et al. 2007

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

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The structure of intrinsic factor (IF) in complex with cobalamin (Cbl) was determined at 2.6-Å resolution. The overall fold of the molecule is that of an ␣6/␣6 barrel. It is a two-domain protein, and the Cbl is bound at the interface of the domains in a base-on conformation. Surprisingly, two full-length molecules, each comprising an ␣-and a ␤-domain and one Cbl, and two truncated molecules with only an ␣-domain are present in the same asymmetric unit. The environment around Cbl is dominated by uncharged residues, and the sixth coordinate position of Co 2؉ is empty. A detailed comparison between the IF-B12 complex and another Cbl transport protein complex, trans-Cbl-B12, has been made. The pH effect on the binding of Cbl analogues in transport proteins is analyzed. A possible basis for the lack of interchangeability of human and rat IF receptors is presented.5] is a water-soluble vitamin and is essential for the growth and development of all mammals, including humans. Cbl is a member of the corrinoid series of cobalt-containing compounds and is distinguished from some other members of this group by possessing a nucleotide side chain terminating in dimethylbenzimidazole (1, 2). It serves as a key enzymatic cofactor for a number of methyltransferase and mutase reactions occurring in nature (3). In mammals, it contributes the prosthetic group for two important enzymes, methionine synthase (a methyltransferase) and methylmalonylCoA mutase (1, 2, 4).In mammals, three proteins are involved in the uptake, transport, and storage of Cbl. These are gastric intrinsic factor (IF), trans-Cbl II (TC), and haptocorrin (HC). These are immunologically distinct proteins with a protein core of Ϸ46 kDa. IF and HC are heavily glycosylated, but TC is not (5, 6). In humans, the genes for IF and HC are located in chromosome 22 (7,8), whereas the gene for TC is located in chromosome 11 (9). Human IF contains 399-aa residues plus Ϸ15% carbohydrate, giving it a molecular mass of Ϸ60 kDa, as observed by gel filtration (10-13). All three proteins promote Cbl entry through endocytosis involving distinct cell surface receptors (5,(14)(15)(16)(17)(18)(19)(20).Dietary Cbl is bound first to HC in the gastric lumen but is transferred to IF in the duodenum after degradation of HC by pancreatic proteases. IF is responsible for transit of Cbl through the small intestine and delivery of it to the endothelial cells that line the ileum. The IF-Cbl complex is then recognized by the IF-Cbl receptor, cubilin (CUB), located on the luminal side of the intestinal mucosal cells, and mediates its internalization. Lysosomal degradation of the internalized IF-Cbl complex releases Cbl, which is then able to bind to TC, probably within the enterocyte. The TC-Cbl complex is then translocated across the basolateral membrane and released into the circulation, to be taken up by TC-Cbl receptor-mediated process by all cells in the body. Lysosomal dissociation of the complex then occurs along with transfer of Cbl to the coenzyme methyl-and Ado-Cbl in the cytoplasm and i...

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Section: Discussionmentioning

confidence: 99%

Crystal structure of human intrinsic factor: Cobalamin complex at 2.6-Å resolution

Mathews¹,

Gordon

Chen³

et al. 2007

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

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“…A Biacore CM5 dextran sensor chip was activated with N-hydroxysuccinimide and N-ethyl carbodiimide according to manufacturer protocols and cubilin (in 10 mM acetate, pH 4.8) was injected immediately afterward. Unreacted sites were blocked with 1 M ethanolamine (pH 8.5) (9,16,20,22). When a control (reference) surface was needed for quantitative measurements, an equal amount of casein (0.20 mg/ml in 10 mM acetate, pH 4.78) was immobilized in a parallel flow cell.…”

Section: Methodsmentioning

confidence: 99%

“…Mechanistic studies on renal tubular proteins demonstrate that light chains, independent of their source, consistently bind to cubilin in the proximal tubule (2) and to Tamm-Horsfall protein in the distal tubule (11). Cubilin (gp280) is a giant glycoprotein receptor and peripheral membrane protein, abundant in the clefts between apical brush-border membrane microvilli (2,16,18). Tamm-Horsfall protein is a glycoprotein secretory product of the ascending limb of the loop of Henle (11).…”

mentioning

confidence: 99%

“…Saito et al (19) cloned the protein, finding a 5,044-residue protein with high homology to the low-density lipoprotein receptor family. The structure of cubilin, a 460-kDa protein, is characterized by 27 consecutive low-affinity ligand binding domains (2, 4), followed by 8 EGF repeats, but no transmembrane span (16). Cubilin is a peripheral membrane protein anchored to the apical membrane of proximal tubule cells via attachment to megalin (16).…”

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confidence: 99%

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Light chains are a ligand for megalin

Klassen¹,

Allen²,

Batuman³

et al. 2005

Journal of Applied Physiology

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“…The present study was initiated to identify ligands to cubilin, the 460-kDa receptor known to function as the intrinsic factorvitamin B 12 ) receptor in the intestine (11,12) and in kidney and yolk sac as the high-affinity apolipoprotein-A1͞HDL receptor (13,14) and low-affinity albumin receptor (15). Cubilin lacks a classical transmembrane region, and the membrane trafficking of cubilin is suggested to be assisted by megalin (16), which colocalizes with and binds to cubilin (11).…”

mentioning

confidence: 99%

Megalin-dependent cubilin-mediated endocytosis is a major pathway for the apical uptake of transferrin in polarized epithelia

Kozyraki

Fyfe

Verroust

et al. 2001

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

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211

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Cubilin is a 460-kDa protein functioning as an endocytic receptor for intrinsic factor vitamin B 12 complex in the intestine and as a receptor for apolipoprotein A1 and albumin reabsorption in the kidney proximal tubules and the yolk sac. In the present study, we report the identification of cubilin as a novel transferrin (Tf) receptor involved in catabolism of Tf. Consistent with a cubilinmediated endocytosis of Tf in the kidney, lysosomes of human, dog, and mouse renal proximal tubules strongly accumulate Tf, whereas no Tf is detectable in the endocytic apparatus of the renal tubule epithelium of dogs with deficient surface expression of cubilin. As a consequence, these dogs excrete increased amounts of Tf in the urine. Mice with deficient synthesis of megalin, the putative coreceptor colocalizing with cubilin, also excrete high amounts of Tf and fail to internalize Tf in their proximal tubules. However, in contrast to the dogs with the defective cubilin expression, the megalin-deficient mice accumulate Tf on the luminal cubilin-expressing surface of the proximal tubule epithelium. This observation indicates that megalin deficiency causes failure in internalization of the cubilin-ligand complex. The megalin-dependent, cubilin-mediated endocytosis of Tf and the potential of the receptors thereby to facilitate iron uptake were further confirmed by analyzing the uptake of 125 I-and 59 Fe-labeled Tf in cultured yolk sac cells.

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The Intrinsic Factor-Vitamin B12 Receptor and Target of Teratogenic Antibodies Is a Megalin-binding Peripheral Membrane Protein with Homology to Developmental Proteins

Cited by 238 publications

References 44 publications

Crystal structure of human intrinsic factor: Cobalamin complex at 2.6-Å resolution

Crystal structure of human intrinsic factor: Cobalamin complex at 2.6-Å resolution

Light chains are a ligand for megalin

Megalin-dependent cubilin-mediated endocytosis is a major pathway for the apical uptake of transferrin in polarized epithelia

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