A structural model of human erythrocyte band 2.1: alignment of chemical and functional domains.

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Abstract
Protein 2.1 is a 210-kilodalton protein that connects erythrocyte spectrin to the NH2-terminal cytoplasmic domain of band 3 and thereby functions as the essential linkage between the membrane skeleton and the bilayer. This protein was cleaved into specific chemical domains by limited digestion with trypsin and .alpha.-chymotrypsin at 0.degree. C. Intermediate-sized peptides were separated by 2-dimensional isoelectric focusing/NaDodSO4[sodium dodecyl sulfate]/polyacrylamide gel electrophoresis and characterized by high resolution peptide mapping. A provisional structural model of protein 2.1 was established by comparing the peptide maps of these chemical domains to maps obtained from larger overlapping chymotryptic fragments as well as fragments obtained from 2-nitro-5-thiocyanobenzoic acid cleavage. In addition to providing a provisional structural map of protein 2.1, 2 functional domains of protein 2.1, an 83-kilodalton tryptic peptide (T-83) which binds band 3 and a 65-kilodalton tryptic peptide (T-65) which binds spectrin were identified. The functional domains were localized along the linear map of protein 2.1.