Identification of functional domains of human erythrocyte spectrin.

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Abstract
Isolated human erythrocyte spectrin in a dimer of 2 unique polypeptide chains. The dimer (.alpha..beta.) undergoes reversible salt- and temperature-dependent association to form (.alpha..beta.)2 tetramers. Spectrin also binds with high affinity to a protein receptor on the cytoplasmic surface of erythrocyte membrane vesicles. By cleavage of spectrin at its cysteine residues with 2-nitro-5-thiocyanobenzoic acid, a 50,000 dalton peptide fragment was isolated which inhibits the binding of spectrin to erythrocyte membrane vesicles. This peptide arises from a terminal region of the .beta. chain. An 80,000 dalton peptide generated by restricted trypsin digestion binds preferentially to dimeric spectrin. This peptide arises from a terminal portion of the .alpha. chain. Multiple peptides involved in noncovalent associations between the chains were also identified. These associations indicate that the 2 subunits of spectrin are aligned parallel to one another and that the tetramer formation site and the high-affinity membrane binding site are in close proximity to one another.