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Cobalamin transport proteins and their cell-surface receptors

Published online by Cambridge University Press:  13 February 2004

Bellur Seetharam  and
Raghunatha R. Yammani
Bellur Seetharam
Affiliation:
Division of Gastroenterology and Hepatology, Departments of Medicine and Biochemistry, Medical College of Wisconsin and Clement Zablocki Veterans Medical Center, Milwaukee, WI 53295, USA.
Raghunatha R. Yammani
Affiliation:
Division of Gastroenterology and Hepatology, Departments of Medicine and Biochemistry, Medical College of Wisconsin and Clement Zablocki Veterans Medical Center, Milwaukee, WI 53295, USA.
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Abstract

The primary function of cobalamin (Cbl; vitamin B12) is the formation of red blood cells and the maintenance of a healthy nervous system. Before cells can utilise dietary Cbl, the vitamin must undergo cellular transport using two distinct receptor-mediated events. First, dietary Cbl bound to gastric intrinsic factor (IF) is taken up from the apical pole of ileal epithelial cells via a 460 kDa receptor, cubilin, and is transported across the cell bound to another Cbl-binding protein, transcobalamin II (TC II). Second, plasma TC II–Cbl is taken up by cells that need Cbl via the TC II receptor (TC II-R), a 62 kDa protein that is expressed as a functional dimer in cellular plasma membranes. Human Cbl deficiency can develop as a result of acquired or inherited dysfunction in either of these two transmembrane transport events. This review focuses on the biochemical, cellular and molecular aspects of IF and TC II and their cell-surface receptors.

Keywords

cobalaminvitamin B12Intrinsic factorCubilintranscobalamin IItranscobalamin II-receptorendocytosis
Type
Review Article
Information
Expert Reviews in Molecular Medicine , Volume 5 , Issue 18 , 13 June 2003 , pp. 1 - 18
Copyright
© Cambridge University Press 2003

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