Cubilin-amnionless receptor complex (Cubam)

The Cubilin-amnionless receptor complex, commonly known as Cubam, is a multimeric endocytic receptor essential for the absorption of specific ligands in the intestine and kidney [1, 3]. It is composed of two primary subunits: cubilin, which provides the ligand-binding domains, and amnionless, which anchors the complex to the plasma membrane and initiates endocytosis [2, 5]. In the terminal ileum, Cubam is the sole receptor responsible for the uptake of the intrinsic factor-vitamin B12 complex, a process vital for maintaining systemic cobalamin levels [1, 4]. In the renal proximal tubules, the complex facilitates the reabsorption of various proteins from the glomerular filtrate, including albumin and transferrin, to prevent proteinuria [3, 4]. Mutations in the genes encoding either subunit result in Imerslund-Gräsbeck syndrome, characterized by megaloblastic anemia and persistent proteinuria [1, 6]. While not a typical target for pharmacological inhibition, Cubam is the primary pathway for the therapeutic administration of oral vitamin B12 [8]. Furthermore, its role in protein trafficking makes it a subject of interest for targeted drug delivery and a potential biomarker for renal health and certain malignancies [2, 4].

Other names

Cubam receptorIntrinsic factor-vitamin B12 receptorIF-B12 receptorCubilin-amnionless complexCUBN-AMN complex

The receptor complex facilitates the receptor-mediated endocytosis of the intrinsic factor-vitamin B12 complex in the ileum and the reabsorption of low-molecular-weight proteins in the renal proximal tubules [1, 3, 4].