Molecular heterogeneity of hereditary pyropoikilocytosis: identification of a second variant of the spectrin alpha-subunit

Abstract

In hereditary pyropoikilocytosis (HPP), the red cell membrane skeletons exhibit a mechanical instability that can be correlated to defective self-association of spectrin heterodimers. To determine the underlying molecular defect, we have subjected HPP spectrin to limited tryptic digestion, followed by one- and two-dimensional separations of the peptides. Two of the HPP kindreds exhibited a marked decrease in 80,000- dalton peptide (previously identified as the spectrin dimer-dimer contact domain of the alpha-subunit) and a concomitant increase of the 74,000-dalton polypeptide (presumably derived from the 80,000-dalton domain) and a decrease in a 22,000-dalton polypeptide. We now report tryptic digests of two other HPP kindred that are characterized by a decrease or complete absence of the 80,000-dalton tryptic fragment, with a concomitant increase in fragments at 46,000 and 17,000 daltons. The 46,000-dalton fragment separated into multiple spots on isoelectric focusing, ranging in isoelectric point from 5.25 to 5.35, and the 17,000-dalton fragment focused to a single spot at 5.4. Minor fragments at 56,000 and 22,000 daltons were also decreased, while a 38,000-dalton fragment increased. Limited tryptic digestion of the separated alpha- and beta-subunits revealed that the 74,000-dalton fragment in the first group of patients and the 46,000-dalton fragment in the second group of patients were derived from the alpha-subunit. Both subtypes exhibited a similar defect of spectrin self-association, with 30%-38% of spectrin dimers in O degrees C extracts. The results indicate that at least two distinct forms of structurally defective spectrin may give rise to the clinical presentation of HPP.

Spα1/65 hereditary elliptocytosis in North Africa

“…We hypothesize that the degree to which the 65,000-dalton fragment will appear depends on the type of 0-chain the mutated a-chain is combined with. It is known that isolated a-chains of patients displaying HE do not behave differently from normal a-chains [8,24]. We have recently detected a shortened variant of the @chain that is associated with and, presumably, responsible for an increase of the 74,000-dalton fragment (Pothier et al, submitted).…”

Defective spectrin dimer self‐association in thalassemic red cells

“…We report a defective association 6f spectrin dimers to tetramers in thalassemic red cells both with and without hemoglobin variants commonly found in Southeast Asia. 15 healthy volunteers (20-25 yr of age) with normal hemoglobin typing and hematologic profile and 57 subjects (12-54 yr) with a variety of hemoglobinopathies were studied: 7 cases of a-thalassemia (a-thal) trait, 9 cases of Hb H disease (a-thal l/a-thal 2), 11 cases of Hb H with Hb Constant Spring (CS) (a-thal 1/Hb CS) (2 splenectomised), 6 cases of (3-thalassemia (B-thal) trait, 5 cases of homozygous (3-thal (2 were splenectomized), 11 cases of (3O-thal with Hb E (Pothal/Hb E) (2 were splenectomized), 1 case of (3'thal/Hb E, 4 carriers of H b E , 2 cases of homozygous Hb E and 1 case of combined a-thal 1/Hb CS and Hb E (AE Bart's disease). Criteria for diagnosis were based on hemoglobin typing and hematologic profile of families, as previously described (18).…”