A NEW ABNORMAL VARIANT OF SPECTRIN IN BLACK PATIENTS WITH HEREDITARY ELLIPTOCYTOSIS

  • 1 January 1985
    • journal article
    • research article
    • Vol. 65  (5) , 1208-1217
Abstract
Seven black patients with mild hereditary elliptocytosis (HE) from 5 unrelated families were studied. The erythrocytes of these patients exhibited an abnormal thermal sensitivity (between 45.degree. C and 47.degree. C instead of 49.degree. C). An important defect of spectrin dimer self-association was detected in 2 ways: the proportions of spectrin dimer (SpD) extracted from membranes at 4.degree. C under low ionic strength conditions were increased between 25 and 56% (normal value 15% .+-. 2%); the spectrin dimer .fwdarw. tetramer conversion in solution were defective with an association constant value between 0.4 and 2.4 .times. 105 M-1 for a normal value of 6 .+-. 0.4 .times. 105 M-1. Spectrin (Sp) from HE patients and normal volunteers (32 black and 22 white subjects) was submitted to limited tryptic digestion, followed by 1- or 2-dimensional separation of the peptides. Peptide patterns of crude Sp from all 7 HE patients exhibited a marked and reproducible decrease in 80,000 dalton peptide (previously identified as the dimer-dimer interaction domain of the .alpha.-chain) and a concomitant appearance of a novel 65,000 dalton peptide. A minor fragment at 28,000 daltons was also decreased. Tryptic digestion of HE spectrin dimer and tetrameter (SpT), isolated after the SpD self-association procedure in solution, revealed modifications (decrease in the 80,000 dalton peptide and presence of a 65,000 dalton peptide) predominantly in HE SpD when peptide patterns of HE SpT were quite similar to control SpT patterns. Immunoblots with anti-.alpha.-chain antibodies revealed that the 65,000 dalton peptide derived from the .alpha.-chain. Kinetic studies of Sp digestion showed that the 65,000 dalton peptide did not result from further digestion of a 74,000 intermediate and was not a precursor of 46,000-50,000 dalton peptides. These results show a new structural defect of Sp-.alpha.-chain, associated with a defective Sp dimer self-association in HE.