Crystal structure of human Band3 (anion exchanger)

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Anion exchanger (AE) gene family consists of four members, AE1-4. These AE proteins are present in most cells and regulate intracellular pH and chloride (Cl-) by the exchange transport of anions across membranes. Band 3, designated AE1, is the major integral membrane protein of the red blood cells and intercalated cells of the distal and collecting tubules of the kidney. Band 3, consisting of 911 amino acids, has two principal structural domains. Its 40 kDa N-terminal domain in the cytoplasm binds the red blood cell skeleton proteins and has a role in maintaining the shape of erythrocytes. While the membrane domain of human erythrocyte Band3 works as a Cl^-/HCO_3^- antiporter. This exchange is a key step for CO_2/O_2 circulation in the blood. In spite of their importance, structural information about Band3 is still unknown. We used X-ray crystallography to solve the three-dimensional structure of Band3, fixed in an outward-open conformation by cross-linking, at 3.4Å resolution. Band3 are formed as a dimmer in complex with Fab fragments. There are V-shaped densities near the center of the dimmer.