Modulation of lateral mobility of band 3 in the red cell membrane by oxidative cross-linking of spectrin

Abstract

Several recent studies have shown that the lateral diffusion of erythrocyte transmembrane proteins is modulated by the sub-membrane network of spectrin, actin and polypeptide 4.1 (refs 1–3). The rate of lateral diffusion of the major transmembrane glycoprotein (the anion transport channel, band 3) is increased approximately 50-fold in membranes from spherocytic eryth-rocytes of mice which are deficient in the membrane skeletal protein spectrin¹. Lateral mobility is increased when spectrin is removed from the membrane by extraction at low ionic strength² or when it is displaced by a fragment of ankyrin containing the membrane attachment site for spectrin³. Such experiments show that the presence of spectrin on the membrane restricts the mobility of membrane proteins, but they do not define the mechanism by which spectrin could modulate membrane protein mobility in situ. The oxidant diamide has been shown to cross-link spectrin via intermolecular disulphide coupling into a high molecular weight complex⁴ and this is associated with inhibition of discocyte–echinocyte shape change⁵ and decreased erythrocyte deformability⁶. Here we report that the lateral mobility of band 3 protein is decreased in erythrocytes in which spectrin is cross-linked via diamide. Furthermore, this inhibition of mobility is reversed when spectrin oxidative cross-links are reduced by addition of dithiothreitol (DTT).