The structural basis of ankyrin function. II. Identification of two functional domains.
Human erythrocyte ankyrin was cleaved by restricted proteolysis at 0 degrees C into two distinct chemical domains. The site on ankyrin that binds spectrin was found to be within a 55,000-dalton domain by spectrin affinity chromatography and co-sedimentation with spectrin in a sucrose gradient. A 32,000-dalton fragment of this domain was prepared (tryptic digest, 0 degrees C, 24 h), separated by gel filtration, and shown to inhibit spectrin binding to the membrane. By comparison with previous two-dimensional peptide maps, the spectrin-binding site was located within this 32,000-dalton fragment near the end of the molecule. The band 3-binding site was identified within an 82,000-dalton domain by binding to a band 3 affinity column. Gel electrophoresis in the absence of detergents confirmed these results and demonstrated that a peptide from the cytoplasmic portion of band 3 retained the capacity to bind the 82,000-dalton domain. The binding properties of the structural domains of ankyrin were correlated with a determination of the affinity constant of the intact molecule. Ankyrin bound with a high affinity to the cytoplasmic portion of band 3 (KD = 8 X 10(-8) M) and to spectrin tetramer (KD = 1 X 10(-7) M) but less so to spectrin dimer (KD = 1 X 10(-6) M). These findings are summarized in a preliminary structural and functional model of ankyrin's role in linking spectrin to the membrane.
D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism; D017487:Ankyrins; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism*; D010446:Peptide Fragments / Q000032:analysis; D011485:Protein Binding; D013049:Spectrin / Q000378:metabolism
D001457:Anion Exchange Protein 1, Erythrocyte; D017487:Ankyrins; D008565:Membrane Proteins; D010446:Peptide Fragments; D013049:Spectrin