Chapter 8 Actin—Membrane Interactions in Eukaryotic Mammalian Cells

Publisher Summary Actin assembles reversibly into linear polymers, and a large number of actin-binding proteins regulate this assembly and influence the architecture of actin filaments to produce a wide variety of three-dimensional structures. Actin and this family of actin-binding proteins constitute “the actin system.” Actin tends to concentrate in the periphery of cells in general and is, therefore, close to the plasma membrane, the shape of which it presumably influences and where it in turn can be regulated by signals generated by the interaction of membrane receptors with extracellular ligands. Although spectrin, a rodlike protein that assembles into tetramers, constitutes the principal mass of protein, in protein network that laminates the membrane of the red blood cell, actin oligomers (along with other proteins) link the spectrin molecules and therefore this cytoskeleton can be considered to be a member of the actin system. Molecules that bear names, such as fodrin and terminal web (TW) 260/240, contain epitopes immunoreactive with spectrin and resemble erythroid spectrin in size and shape. These properties as well as the presence in nonerythroid cells of proteins resembling ankyrin (the link between erythrocyte spectrin and band 3) in addition to other erythroid protein analogs, have led researchers to search for a “membrane skeleton” analogous to the spectrin–actin shell in eukaryotic cells.