Binding of intrinsic factor to ileal brush border membrane in the rat

Seetharam, Bellur; Bakke, James E.; Alpers, David H.

doi:10.1016/0006-291x(83)90995-6

Cited by 39 publications

(11 citation statements)

References 14 publications

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“…Although human and rat IF share 80% sequence identity, human IF does not bind to the rat IF receptor (40). Only 6 of the 37 residues implicated in the receptor-binding region (residues 25-62) differ between human and rat IF (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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“…FluoroHance TM used for autoradiography was obtained from Research Products International Corp. (Mount Prospect, IL). Rat gastric intrinsic factor used in the current studies was purified from the rat stomach as described previously (15). Antiserum to purified rat renal cubilin raised in rabbits was prepared as described previously (4).…”

Section: Methodsmentioning

confidence: 99%

Identification and Characterization of Two Distinct Ligand Binding Regions of Cubilin

Yammani

Seetharam

2001

Journal of Biological Chemistry

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“…IF used in these studies was prepared from the rat stomach as described earlier (33). Antiserum to purified rat megalin was raised in New Zealand white rabbits as described earlier (39).…”

Section: Methodsmentioning

confidence: 99%

Loss of albumin and megalin binding to renal cubilin in rats results in albuminuria after total body irradiation

Yammani

Sharma

Seetharam

et al. 2002

American Journal of Physiology-Regulatory, Integrative and Comp

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. Loss of albumin and megalin binding to renal cubilin in rats results in albuminuria after total body irradiation. Am J Physiol Regulatory Integrative Comp Physiol 283: R339-R346, 2002. First published April 4, 2002 10.1152/ajpregu.00752.2001.-The role of the renal apical brush-border membrane (BBM) endocytic receptors cubilin and megalin in the onset of albuminuria in rats exposed to a single dose of total body irradiation (TBI) has been investigated. Albuminuria was evident as immunoblot (IB) analysis of the urine samples from TBI rats revealed excretion of large amounts of albumin. IB analysis of the BBM proteins did not reveal any significant changes in cubilin or megalin levels, but 125 I-albumin binding to BBM from TBI rats declined by 80% with a fivefold decrease (from 0.5 to 2.5 M) in the affinity for albumin. IB analysis of cubilin from the BBM demonstrated a 75% loss when purified using albumin, but not intrinsic factor (IF)-cobalamin (Cbl) ligand affinity chromatography. Immunoprecipitation (IP) of Triton X-100 extract of the BBM with antiserum to cubilin followed by IB of the immune complex with an antiserum to megalin revealed a 75% loss of association between megalin and cubilin. IP studies with antiserum to cubilin or megalin and IB with antiserum to the cation-independent mannose 6-phosphate/insulin-like growth factor II-receptor (CIMPR) revealed that CIMPR interacted with both cubilin and megalin. In addition, TBI did not disrupt the association of CIMPR with either cubilin or megalin in BBM. These results suggest that albuminuria noted in TBI rats is due to selective loss of albumin and megalin, but not CIMPR or IF-Cbl binding by cubilin. Furthermore, these results also suggest that albumin and IF-Cbl binding to cubilin occur at distinct sites and that in the rat renal BBM, CIMPR interacts with both cubilin and megalin.

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Binding of intrinsic factor to ileal brush border membrane in the rat

Cited by 39 publications

References 14 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

Identification and Characterization of Two Distinct Ligand Binding Regions of Cubilin

Loss of albumin and megalin binding to renal cubilin in rats results in albuminuria after total body irradiation

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