Keratin filaments form obligatory heterodimers consisting of one type I and one type II keratin that build the intermediate filaments (IF). These filaments mediate resilience and mechanical strength to epithelial cells and maintain tissue integrity. Specific type I/type II pairs are co-expressed in vivo and serve as markers for distinct tissue layers and cell differentiation states. Heterodimerization has been regarded the undisrupted hallmark of IF. We show now that recombinantly expressed cytokeratin 16 (K16) interacts with itself and forms homodimers even in denaturating SDS-PAGE analysis. Detailed FRET experiments in HaCaT keratinocytes were in accordance with our in vitro observations and showed clearly that K16 is able to form strong homodimers. Homotypic keratin interactions has been previously shown for keratin 17 (K17) and keratin 18 (K18) by Schnabel et al. (Biochim Biophys Acta, 1998: 1403: 158), and we now proved K16 to be the third type I keratin that is able to form homodimers.
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Fluorescence Resonance Energy Transfer
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