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J Cell Biol. 1983 Oct 1; 97(4): 1131–1143.
doi: 10.1083/jcb.97.4.1131
PMCID: PMC2112608
PMID: 6194161

The fibrillar substructure of keratin filaments unraveled

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Abstract

We show that intermediate-sized filaments reconstituted from human epidermal keratins appear unraveled in the presence of phosphate ions. In such unraveling filaments, up to four "4.5-nm protofibrils" can be distinguished, which are helically twisted around each other in a right- handed sense. Lowering the pH of phosphate-containing preparations causes the unraveling filaments to further dissociate into "2-nm protofilaments." In addition, we find that reconstitution of keratin extracts in the presence of small amounts of trypsin yields paracrystalline arrays of 4.5-nm protofibrils with a prominent 5.4-nm axial repeat. Limited proteolysis of intact filaments immobilized on an electron microscope grid also unveils the presence of 4.5-nm protofibrils within the filament with the same 5.4-nm axial repeat. These results, together with other published data, are consistent with a 10-nm filament model based on three distinct levels of helical organization: (a) the 2-nm protofilament, consisting of multi-chain extended alpha-helical segments coiled around each other; (b) the 4.5- nm protofibril, being a multi-stranded helix of protofilaments; and (c) the 10-nm filament, being a four-stranded helix of protofibrils.

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Selected References

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