The spectrin-actin complex and erythrocyte shape.

Abstract

AbstractThe effects of phosphorylation of spectrin on the properties of the cytoskeletal network of the human erythrocyte have been studied. A suspension of the cytoskeletal residues obtained after extraction of the ghosts with the nonionic detergent Triton X‐100 forms a gel on addition of membrane kinase and ATP. Phosphorylation has no effect on the association state of purified spectrin. No species higher than a tetramer of polypeptide chains is formed in vitro; in the absence of divalent cations, this tetramer is an entity liberated from and evidently present in the membrane. It has not so far proved possible to detect any F‐actin in the cytoskeleton before or after phosphorylation. It is suggested that the consequence of phosphorylation is formation of additional interactions between spectrin and monomeric actin molecules. This view is supported by the formation, after phosphorylation of the Triton‐extracted cytoskeleton, of an insoluble mass of protein on treatment with a cross‐linking reagent. In the absence of divalent cations, a series of oligomeric species is progressively liberated from the cytoskeleton on extraction with solutions of low ionic strength. These oligomers contain actin as well as spectrin, and are thought to result from disruption of the network by random denaturation of the mono meric actin in the absence of divalent metal ions. A schematic view of the effects of phosphorylation on the structure of the cytoskeleton is presented.