Cubilin-amnionless complex (CUBAM)

The Cubilin-amnionless complex (CUBAM) is a specialized endocytic receptor system essential for nutrient absorption and renal protein salvage. It consists of Cubilin, a large peripheral membrane protein containing multiple CUB and EGF-like domains, and Amnionless, a transmembrane protein that anchors Cubilin to the cell surface and mediates its internalization. Primarily located in the ileum and renal proximal tubules, the CUBAM complex is the definitive receptor for the intrinsic factor-vitamin B12 complex, facilitating its uptake into the bloodstream. In the kidney, it functions in tandem with Megalin to reabsorb a wide array of filtered ligands, including albumin, transferrin, and vitamin D-binding protein, thereby preventing their loss in urine. Genetic defects in either component of the complex result in Imerslund-Gräsbeck syndrome, a condition marked by megaloblastic anemia and persistent proteinuria. Due to its high specificity and endocytic capacity, the complex is a subject of interest for targeted drug delivery and serves as a significant prognostic biomarker in certain cancers, such as renal cell carcinoma.

Other names

CUBAMIntrinsic factor-cobalamin receptorIFCRgp280MGA1Cubilin complex

Receptor-mediated endocytosis of ligands followed by lysosomal processing or transcytosis