Cryoelectron Microscopy of Red Cell Skeletons Reveals that Spectrin has a Helical Conformation

Abstract

Abstract In vivo the red blood cell reversibly and rapidly deforms as it passes through the small capillaries. Although the physiochemical basis of the red cell's deformability is unknown, it is regarded as being a property of the membrane protein spectrin. We have used cryoelectron microscopy to study the structure of spectrin in membrane skeletons to determine how its molecular structure confers elastic properties on the cell membrane. Cryomicroscopy has the virtue of minimally perturbing easily deformable structures such as spectrin. Figure 1 is an electron micrograph of a portion of a frozen-hydrated red cell skeleton. The spectrin molecules are indicated by the arrow heads. They cross link the skeletal network by interacting with short rod like segments F-actin (indicated by the arrows) containing about 13 actin molecules. In such micrographs the spectrin appears to have a sinusoidal shape whereas in negatively stained preparations spectrin appears to be straight. We have used the procedure of Margalef in order to determine the three dimensional trajectory of the spectrin molecule.