Intrinsic factor-vitamin B12 receptor (Cubilin-AMN complex) (Cubilin-AMN (Cubam) receptor)

The Intrinsic factor-vitamin B12 receptor (also known as the Cubilin-AMN complex or Cubam receptor) is a large multimeric endocytic receptor found principally on the apical surface of ileal enterocytes and renal tubular cells. It consists of the peripheral cubilin protein (comprised of multiple CUB domains and EGF-like repeats) and a transmembrane partner, amnionless (AMN). This receptor specifically mediates the uptake of vitamin B12 when complexed with intrinsic factor—a glycoprotein necessary for dietary vitamin B12 absorption. Upon binding, the receptor complex facilitates endocytosis, delivering vitamin B12 into the enterocyte for subsequent transport into the systemic circulation. Molecular defects in either component of the receptor cause selective malabsorption of vitamin B12 and often proteinuria, exemplified by Imerslund-Gräsbeck syndrome. Radiolabeled vitamin B12 analogs are often used experimentally and clinically to visualize or quantify B12 uptake, but the radiolabel itself is not a target molecule or receptor.

Other names

Cubilin-AMN complexCubam receptorIF-B12 receptorIntrinsic factor receptor

Vitamin B12 bound to intrinsic factor is recognized and internalized via receptor-mediated endocytosis by the cubilin-AMN complex on ileal enterocytes