Basis of unique red cell membrane properties in hereditary ovalocytosis

Abstract

Hereditary ovalocytes from a Mauritian subject are extremely rigid, with a shear elastic modulus about three times that of normal cells, and have increased resistance to invasion by the malaria parasite Plasmodium falciparum in vitro. The genetic anomaly resides in band 3; the protein gives rise to chymotryptic fragments with reduced mobility in SDS/polyacrylamide gel electrophoresis, but this is a result of anomalous binding of SDS and not a higher molecular weight. Analysis of the band 3 gene reveals (1) a point mutation (Lys56 → Glu), which also occurs in a common asymptomatic band 3 (Memphis) variant and governs the electrophoretic properties, and (2) a deletion of nine amino acid residues, including a proline residue, encompassing the interface between the membrane-associated and the N-terminal cytoplasmic domains. The interaction of the mutant band 3 with ankyrin appears unperturbed. The fraction of band 3 capable of undergoing translation diffusion in the membrane is greatly reduced in the ovalocytes. Cells containing the asymptomatic band 3 variant were normal with respect to all the properties that we have studied. Possible mechanisms by which a structural change in band 3 at the membrane interface could regulate rigidity are examined.