On the structure of erythrocyte spectrin in partially expanded membrane skeletons

Spectrin is generally believed to play an important role in the erythrocyte membrane's ability to deform elastically. We have studied the structure of negatively stained spectrin in partially expanded membrane skeletons to determine how its molecular structure confers elastic properties on the cell membrane. Fourier analysis of electron micrographs of spectrin reveals that the alpha and beta subunits are twisted about a common axis, forming a two-start helix with twofold rotational symmetry. We propose that elastic deformation of the cell is mediated by transient extension of the helix by mechanical forces.