Defective binding of spectrin to ankyrin in a kindred with recessively inherited hereditary elliptocytosis.

Abstract

Astract. The interaction of spectrin with spectrin-depleted inside-out membrane vesicles was studied in a kindred with an atypical variant of hereditary elliptocytosis inherited in a recessive manner. The probands are characterized by prominent elliptocytosis, decreased erythrocyte thermal stability, an altered limited tryptic peptide pattern of spectrin digested at low ionic strength, and defective spectrin dimer-dimer association. The parents are normal. The spectrin/band 3 ratio determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of isolated membranes of the probands was decreased to -70% of control values, and total erythrocyte spectrin content in one proband was also decreased on SDS-PAGE. When a monospecific antispectrin antibody was used, a faintly labeled fragment of molecular weight -28,000 was detected on immunoblots of whole cell lysates of one proband and a control, but could not account for the decreased erythrocyte spectrin content of the proband on SDS-PAGE. Binding and competitive inhibition studies revealed an alteration in the spectrin-ankyrin interaction due to an abnormality of spectrin in the probands. No defect was found in the mother; the father's spectrin showed decreased binding affinity, although it was not so severe as in the probands. Separation of bound and unbound spectrin dimers from one proband and subsequent conversion to tetramers showed that the self-association defect was detectable only on the bound subpopulation of her spectrin. These findings demonstrate a hitherto undescribed functional abnormality of spectrin in this kindred which could result in

Unique alpha-spectrin mutant in a kindred with common hereditary elliptocytosis.

“…PMSF was removed by overnight dialysis at 4°C in 200 vol of 20 mM Tris buffer (pH 8.0) (30). The (6,8,11,12,15 (Fig. 4).…”

“…For example, molecular defects described in kindreds with hereditary elliptocytosis (HE) include a quantitative deficiency of protein 4.1 (4), defective ankyrin-band 3 binding (5), and a number of qualitative defects in spectrin (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). Most of alpha-and betaspectrin defects in HE result in diminished self-association of affected spectrin heterodimers (7)(8)(9)(10)(11)(12)(13)(14)(15)(16), leading to reduced formation of higher molecular weight forms of spectrin and, thus, to skeletal instability. Several previously described defects in alpha spectrin have been distinguished from one another by differing patterns of spectrin peptides generated by limited tryptic digestion (6,(10)(11)(12)(13)(14).…”

“…Most of alpha-and betaspectrin defects in HE result in diminished self-association of affected spectrin heterodimers (7)(8)(9)(10)(11)(12)(13)(14)(15)(16), leading to reduced formation of higher molecular weight forms of spectrin and, thus, to skeletal instability. Several previously described defects in alpha spectrin have been distinguished from one another by differing patterns of spectrin peptides generated by limited tryptic digestion (6,(10)(11)(12)(13)(14). One beta-spectrin mutant exhibited defective binding to ankyrin (1 1), while several others displayed apparent alterations in molecular weight as estimated by SDS polyacrylamide gel electrophoresis (PAGE) (15,16).…”

Multiple protein 4.1 isoforms produced by alternative splicing in human erythroid cells.

“…Dynamic interactions among these proteins allow the circulating erythrocyte to undergo extensive deformation without fragmentation. When the integrity of the membrane skeleton is disrupted by structural abnormalities or deficiencies of its protein components, the membrane becomes susceptible to fragmentation and loses its characteristic discoid shape (7)(8)(9)(10)(11)(12)(13)(14)(15).…”

Partial deficiency of protein 4.1 in hereditary elliptocytosis

“…of one South African black kindred had a defect of spectrin tetramer assembly due to a structural abnormality of the a1 domain of spectrin. The other (C.G., whose family origins were Denmark and Germany) was a compound heterozygote for a defect of spectrin tetramer assembly and a defect in spectrin binding to ankyrin [14].…”