Regulation of the association of membrane skeletal protein 4.1 with glycophorin by a polyphosphoinositide

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Abstract
Many of the physical properties of the erythrocyte membrane appear to depend on the membrane skeleton, which is attached to the membrane through associations with transmembrane proteins1–5. A membrane skeletal protein, protein 4.1, is pivotal in the assembly of the membrane skeleton because of its ability to promote associations between spectrin and actin5–9. Protein 4.1 also binds to the membrane through at least two sites: a high-affinity site on the glycophorins2,10 and a site of lower affinity associated with band 3 (ref. 11). The glycophorin–protein 4.1 association has been proposed to be involved in maintenance of cell shape2,12,13. Here we show that the association between glycophorin and protein 4.1 is regulated by a polyphosphoinositide cofactor. This observation suggests a mechanism which may explain the recently reported dependence of red cell shape on the level of polyphosphoinositides in the membrane14–16.