Large conformational dynamics in Band 3 protein: Significance for erythrocyte senescence signalling

Band 3 (Anion Exchanger 1, AE1), the predominant protein of erythrocyte membranes, facilitates Cl−/HCO3− exchange and anchors the plasma membrane to the cytoskeleton. The Band 3 crystal structure revealed the amino acid 812–830 region as intracellular, conflicting with protein chemical data that suggested extracellular disposition. Further, circulating senescent cell auto-antibody that cannot enter erythrocytes, binds two regions of Band 3: residues 538–554 and 812–830. To reconcile this discrepancy, we assessed localization of residues 812–830 with Band 3 expressed in HEK293 cells and human erythrocytes, using chemical labeling probes and an antibody against residues 812–830. Antibody and chemical probes revealed reorientation of 812–830 region between extracellular and intracellular. This dramatic conformational change is an intrinsic property of the Band 3 molecule, occurring when expressed in HEK293 cells and without the damage that occurs during erythrocyte circulation. Conditions used to crystallize Band 3 for structural determination did not alter conformational dynamics. Collectively, these data reveal large Band 3 conformational dynamics localized to a region previously identified as an erythrocyte senescence epitope. Surface exposure of the senescence epitope (812–830), limited by conformational dynamics, may act as the “molecular clock” in erythrocyte senescence. [Display omitted] •One region of erythrocyte membrane Band 3 protein has controversial topology.•This region binds circulating antibodies to signal cell senescence.•We tested the region's location, using confocal microscopy, and protein chemistry.•The region adopts dramatically different conformations: cytosolic and extracellular.•This conformational change may act as a molecular clock for cell senescence.