Structure of intermediate filaments

• Published in: International journal of biological macromolecules Vol. 5; no. 5; pp. 267 - 274
• Main Authors: Crewther, W.G., Dowling, L.M., Steinert, P.M., Parry, D.A.D.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.1983
• Subjects: coiled-coils; epidermis; intermediate filaments; model structures; Proteins; sequence homologies; α-keratin; Proteins; coiled-coils; model structures; sequence homologies; intermediate filaments; α-keratin; epidermis
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/0141-8130(83)90040-5

Recent amino acid sequence data have revealed that the microfibrils in hard α-keratin contain proteins with highly significant homologies and closely similar structural characteristics to the intermediate filament (IF) proteins known as desmin and vimentin. This result implies that microfibrils in hard α-keratin may be classified as a member of the IF and that the major features of these various filamentous structures are the same. Consequently, data obtained using X-ray diffraction, electron microscopy, amino acid sequence structural analysis and physicochemical techniques have been collated from the hitherto diverse fields of keratin and IF structure and used to formulate a more detailed model for the 7–8 nm diameter filaments than has previously been possible. Two models consisting of four-chain units arranged with the helical symmetry deduced for hard α-keratin 1 (Fraser et al. J. Mol. Biol. 1976, 108, 435–452) are in accord with the data. The structural unit comprises an oppositely directed pair of molecules each consisting of a two-stranded parallel-chain coiled-coil rope of length ∼45 nm stabilized by both interchain and intermolecular ionic interactions. For a perfectly regular structure the filament may be likened either to a seven-stranded cable with a supercoil pitch length of about 345 nm (pitch angle ∼2.9°), or a ten-stranded cable (Fraser, R. D. B. and MacRae, T. P. Polymer 1973, 14, 61–67) with a supercoil pitch length of about 1293 nm (pitch angle ∼0.8°). The models also provide some insight into the self-assembly mechanism of the IF.