Key Concepts of Section 17.4

• Actin filaments are organized by cross-linking proteins that have two F-actin–binding sites. Actin cross-linking proteins can be long or short, rigid or flexible, depending on the type of structure involved (see Figure 17-20).

• Actin filaments are attached laterally to the plasma membrane by specific classes of proteins, as seen in erythrocytes and in cell-surface structures such as microvilli (see Figure 17-21).

• The (+) ends of actin filaments can also be attached to membranes, with assembly mediated between the filament end and the membrane.

• Several diseases have been traced to defects in the microfilament-based cortical cytoskeleton that underlies the plasma membrane.