Molecular and functional changes in spectrin from patients with hereditary pyropoikilocytosis

ties of spectrin from normal and hereditary pyropoiki-locytosis (HPP) donors from the two unrelated families were studied. The structural domains of the spectrin molecule were generated by mild tryptic digestion and analyzed by two-dimensional electrophoresis (isoelec-tric focusing; sodium dodecyl sulfate-polyacrylamide gel electrophoresis). The aI-T80 peptide (Mr 80,000) is not detectable in two related HPP donors; instead, two new peptides (Mr 50,000 and 21,000) are gener-ated and have been identified as fragments of the nor-mal aI-T80. A third sibling has reduced levels of both the normal aI-T80 and the two new peptides. A similar analysis of spectrin from another HPP family indicates that their spectrins contain reduced amounts of the aI-T80 and the 50,000 and 21,000 frag-ments of the aI domain. The HPP donor also has other structural variations in the al, aIl, and alII domains. The aI-T80 domain of normal spectrin has been shown to be an important site for spectrin oligomeriza-tion (J. Morrow and V. T. Marchesi. 1981. J. Cell Biol. 88: 463-468), and in vitro assays indicate that HPP spectrin has an impaired ability to oligomerize. Ghost membranes from HPP donors are also more fragile than membranes from normal erythrocytes when mea-sured by ektacytometry. In both the oligomerization and fragility assays, the degree of impairment is cor-related with the amount of normal aI-T80 present in the spectrin molecule. A preliminary report of this work was presented at a