Erythrocyte Spectrin is Comprised of Many Homologous Triple Helical Segments

Spectrin is an alpha beta heterodimeric protein (molecular weight (Mr) = 460,000) which is a major component of the erythrocyte membrane skeleton. The membrane skeleton also includes actin (band 5) and is attached to the membrane via non-covalent associations with two linking proteins. Recently we have reported the amino acid sequence of a peptide of molecular weight 80,000 which comprises the NH2-terminal one-third of the alpha subunit. This alpha-subunit peptide contains multiple homologous non-identical sequences with a periodicity of 106 amino acids and an approximate molecular weight of 12,000. It was also established that spectrin is not related to any other proteins whose sequence was known. We now report additional amino acid sequence of peptides representative of other domains of both spectrin subunits. The results suggest that most of the human erythrocyte spectrin molecule is comprised of homologous segments with a 106 amino acid (Mr 12,000) length per segment. Each homologous 106-amino acid segment may be folded into a triple helical structure with a short non-helical region connecting adjacent units.