ABSTRACT
This chapter describes that intermediate filaments are much more varied in sequence and structure than either actin filaments or microtubules. Intermediate filaments have an important place in the history of protein structure determination. Genetic engineering experiments in which intermediate filament genes are truncated or point-mutated indicate that sequences close to either end of the central domain are crucial for intermediate filament assembly. Since intermediate filaments are insoluble in buffers whose ionic conditions resemble those of living cytoplasm there must be mechanisms to prevent their subunits associating in an uncontrolled fashion as they are synthesized. Actin and tubulin have been highly conserved in amino acid sequence during evolution and, although they perform many varied functions in cells, changes in the properties of actin filaments or microtubules are conferred by a plethora of actin-binding and microtubule-associated proteins. Desmin is the characteristic intermediate filament of muscle cells. Intermediate filaments are vitally important structural elements for axons in the peripheral nervous system.
