Diversity in protein associations of the spectrin-based membrane skeleton of nonerythroid cells

The purpose of this review is to summarize recent progress in understanding interactions of spectrin with membranes from brain and other tissues. Spectrin has at least two choices in linkages with the membrane, one through ankyrin, which in turn is associated with integral membrane proteins, and another linkage directly with integral membrane sites identified recently in brain membranes. Some of the integral membrane protein sites in brain bind preferentially with one spectrin isoform, while some can interact with both erythroid and the general isoform of spectrin. Ankyrin also has different isoforms, and these exhibit specificity in binding to spectrin isoforms and associate with distinct integral membrane proteins. The membrane binding sites for ankyrin include several integral membrane proteins, which are differentially expressed in different cells: the anion exchanger of intercalated cells of mammalian kidney, the sodium/potassium ATPase of kidney, and the voltage-dependent sodium channel of neurons. Ankyrin is present in many other cell types and it is likely that additional ankyrin-binding proteins will be identified. Each of the proteins that now are candidates for ankyrin binding proteins are ion channels or transporters and are localized in specialized cellular domains. The polarized localization of the ankyrin-associated membrane proteins is an essential aspect of their function at a physiological level. Spectrin and ankyrin thus exhibit an unsuspected diversity in protein linkages and have the potential for cell domain-specific interactions with a variety of membrane proteins.