Important region in the β-spectrin C-terminus for spectrin tetramer formation
Many hereditary hemolytic anemias are due to spectrin mutations at the C-terminal region of β-spectrin (the βC region) that destabilize spectrin tetramer formation. However, little is known about the βC region of spectrin. We have prepared four recombinant β-peptides of different lengths from human erythrocyte spectrin, all starting at position 1898 of the C-terminal region, but terminating at position 2070, 2071, 2072 or 2073. Native polyacrylamide gel electrophoresis showed that the two peptides terminating at positions 2070 and 2071 did not associate with an N-terminal region α-peptide (Spα1-156) in the micromolar range. However, the peptides that terminated at positions 2072 and 2073 associated with the α-peptide. Circular dichroism results showed that the unassociated helices in both α- and β-peptides became associated, presumably to form a helical bundle, for those β-peptides that formed an αβ complex, but not for those β-peptides that did not form an αβ complex. In addition, upon association, an increase in the α-helical content was observed. These results showed that the β-peptides ending prior to residue 2072 (Thr) would not associate with α-peptide, and that no helical bundling of the partial domains was observed. Thus, we suggest that the C-terminal segment of β-spectrin, starting from residue 2073 (Thr), is not critical to spectrin tetramer formation. However, the C-terminal region ending with residue 2072 is important for its association with α-spectrin in forming tetramers.