Question

How do intermediate filaments connect to other cytoskeletal proteins?

Answer 1

Intermediate filament – associated proteins (IFAPs) cross-link intermediate filaments with one another, forming a bundle (also called a tonofilament) or a network, and with other cell structures, including the plasma membrane. Only a few IFAPs have been identified to date, but many more will undoubtedly be discovered as researchers focus attention on the proteins that control IF organization and assembly. Unlike actin-binding proteins or microtubule-associated proteins, none of the known IFAPs sever or cap intermediate filaments, sequester IF proteins in a soluble pool, or act as a motor protein. The organization of intermediate filaments and their supportive function in various cells types depends in large part on their linkage to other cell structures via IFAPs.

A physical linkage between intermediate filaments and microtubules can be detected with certain drugs. Recall that treatment of cells with high concentrations of colchicine causes the complete dissolution of microtubules after a period of several hours (see Figure 19-6). Although vimentin filaments in colchicine-treated cells remain intact, they clump into disorganized bundles near the nucleus. This finding demonstrates that the organization of vimentin filaments is dependent on intact microtubules and suggests the presence of proteins linking the two types of filaments.