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Mouse transcobalamin has features resembling both human transcobalamin and haptocorrin.

Hygum K, Lildballe DL, Greibe EH, Morkbak AL, Poulsen SS, Sorensen BS, Petersen TE, Nexo E - PLoS ONE (2011)

Bottom Line: Subsequent sequencing identified the protein as TC.Analysis of the TC-mRNA level showed a high TC transcript level in these glands and also in the kidney.Our results suggest that the Cbl-binding proteins present in the circulation and exocrine glands may vary amongst species.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Biochemistry, Aarhus University Hospital, Aarhus, Denmark.

ABSTRACT
In humans, the cobalamin (Cbl) -binding protein transcobalamin (TC) transports Cbl from the intestine and into all the cells of the body, whereas the glycoprotein haptocorrin (HC), which is present in both blood and exocrine secretions, is able to bind also corrinoids other than Cbl. The aim of this study is to explore the expression of the Cbl-binding protein HC as well as TC in mice. BLAST analysis showed no homologous gene coding for HC in mice. Submaxillary glands and serum displayed one protein capable of binding Cbl. This Cbl-binding protein was purified from 300 submaxillary glands by affinity chromatography. Subsequent sequencing identified the protein as TC. Further characterization in terms of glycosylation status and binding specificity to the Cbl-analogue cobinamide revealed that mouse TC does not bind Concanavalin A sepharose (like human TC), but is capable of binding cobinamide (like human HC). Antibodies raised against mouse TC identified the protein in secretory cells of the submaxillary gland and in the ducts of the mammary gland, i.e. at locations where HC is also found in humans. Analysis of the TC-mRNA level showed a high TC transcript level in these glands and also in the kidney. By precipitation to insolubilised antibodies against mouse TC, we also showed that >97% of the Cbl-binding capacity and >98% of the Cbl were precipitated in serum. This indicates that TC is the only Cbl-binding protein in the mouse circulation. Our data show that TC but not HC is present in the mouse. Mouse TC is observed in tissues where humans express TC and/or HC. Mouse TC has features in common with both human TC and HC. Our results suggest that the Cbl-binding proteins present in the circulation and exocrine glands may vary amongst species.

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Partial protein sequence alignment of the predicted Cbi-binding region in human proteins.The alignment was done in ClustalW2 using default settings. The region of the three human proteins has previously been predicted to be involved in binding to Cbl and the highlighted residues are the ones expected to be responsible for the binding to Cbl (IF, TC, HC) and other corrinoids (HC only) [24]. For comparison, the similar residue positions in mouse TC are highlighted as well. The numbers in the right margin refer to the specific amino acids of the full-length protein including signal peptides. Complete protein sequence alignment is shown in Supporting Figure S1.
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pone-0020638-g003: Partial protein sequence alignment of the predicted Cbi-binding region in human proteins.The alignment was done in ClustalW2 using default settings. The region of the three human proteins has previously been predicted to be involved in binding to Cbl and the highlighted residues are the ones expected to be responsible for the binding to Cbl (IF, TC, HC) and other corrinoids (HC only) [24]. For comparison, the similar residue positions in mouse TC are highlighted as well. The numbers in the right margin refer to the specific amino acids of the full-length protein including signal peptides. Complete protein sequence alignment is shown in Supporting Figure S1.

Mentions: Figure 3 shows a partial protein sequence alignment of the previously predicted Cbl-binding-region of human HC, TC, and IF [24] and the comparable region of mouse TC. The residues are identical in human TC and mouse TC. Of importance to highlight from the global sequence alignment is that the Cobalt-coordinating histidine-residue in human TC is present in mouse TC (His74).


Mouse transcobalamin has features resembling both human transcobalamin and haptocorrin.

Hygum K, Lildballe DL, Greibe EH, Morkbak AL, Poulsen SS, Sorensen BS, Petersen TE, Nexo E - PLoS ONE (2011)

Partial protein sequence alignment of the predicted Cbi-binding region in human proteins.The alignment was done in ClustalW2 using default settings. The region of the three human proteins has previously been predicted to be involved in binding to Cbl and the highlighted residues are the ones expected to be responsible for the binding to Cbl (IF, TC, HC) and other corrinoids (HC only) [24]. For comparison, the similar residue positions in mouse TC are highlighted as well. The numbers in the right margin refer to the specific amino acids of the full-length protein including signal peptides. Complete protein sequence alignment is shown in Supporting Figure S1.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3105116&req=5

pone-0020638-g003: Partial protein sequence alignment of the predicted Cbi-binding region in human proteins.The alignment was done in ClustalW2 using default settings. The region of the three human proteins has previously been predicted to be involved in binding to Cbl and the highlighted residues are the ones expected to be responsible for the binding to Cbl (IF, TC, HC) and other corrinoids (HC only) [24]. For comparison, the similar residue positions in mouse TC are highlighted as well. The numbers in the right margin refer to the specific amino acids of the full-length protein including signal peptides. Complete protein sequence alignment is shown in Supporting Figure S1.
Mentions: Figure 3 shows a partial protein sequence alignment of the previously predicted Cbl-binding-region of human HC, TC, and IF [24] and the comparable region of mouse TC. The residues are identical in human TC and mouse TC. Of importance to highlight from the global sequence alignment is that the Cobalt-coordinating histidine-residue in human TC is present in mouse TC (His74).

Bottom Line: Subsequent sequencing identified the protein as TC.Analysis of the TC-mRNA level showed a high TC transcript level in these glands and also in the kidney.Our results suggest that the Cbl-binding proteins present in the circulation and exocrine glands may vary amongst species.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Biochemistry, Aarhus University Hospital, Aarhus, Denmark.

ABSTRACT
In humans, the cobalamin (Cbl) -binding protein transcobalamin (TC) transports Cbl from the intestine and into all the cells of the body, whereas the glycoprotein haptocorrin (HC), which is present in both blood and exocrine secretions, is able to bind also corrinoids other than Cbl. The aim of this study is to explore the expression of the Cbl-binding protein HC as well as TC in mice. BLAST analysis showed no homologous gene coding for HC in mice. Submaxillary glands and serum displayed one protein capable of binding Cbl. This Cbl-binding protein was purified from 300 submaxillary glands by affinity chromatography. Subsequent sequencing identified the protein as TC. Further characterization in terms of glycosylation status and binding specificity to the Cbl-analogue cobinamide revealed that mouse TC does not bind Concanavalin A sepharose (like human TC), but is capable of binding cobinamide (like human HC). Antibodies raised against mouse TC identified the protein in secretory cells of the submaxillary gland and in the ducts of the mammary gland, i.e. at locations where HC is also found in humans. Analysis of the TC-mRNA level showed a high TC transcript level in these glands and also in the kidney. By precipitation to insolubilised antibodies against mouse TC, we also showed that >97% of the Cbl-binding capacity and >98% of the Cbl were precipitated in serum. This indicates that TC is the only Cbl-binding protein in the mouse circulation. Our data show that TC but not HC is present in the mouse. Mouse TC is observed in tissues where humans express TC and/or HC. Mouse TC has features in common with both human TC and HC. Our results suggest that the Cbl-binding proteins present in the circulation and exocrine glands may vary amongst species.

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