A small surface hydrophobic stripe in the coiled-coil domain of type I keratins mediates tetramer stability.
Intermediate filaments (IFs) are fibrous polymers encoded by a large family of differentially expressed genes that provide crucial structural support in the cytoplasm and nucleus in higher eukaryotes. The mechanisms involved in bringing together approximately 16 elongated coiled-coil dimers to form an IF are poorly defined. Available evidence suggests that tetramer subunits play a key role during IF assembly and regulation. Through molecular modeling and site-directed mutagenesis, we document a hitherto unnoticed hydrophobic stripe exposed at the surface of coiled-coil keratin heterodimers that contributes to the extraordinary stability of heterotetramers. The inability of K16 to form urea-stable tetramers in vitro correlates with an increase in its turnover rate in vivo. The data presented support a specific conformation for the assembly competent IF tetramer, provide a molecular basis for their differential stability in vitro, and point to the physiological relevance associated with this property in vivo.
Bernot
Kelsie M
KM
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Lee
Chang-Hun
CH
Coulombe
Pierre A
PA
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002478:Cells, Cultured; D002852:Chromatography, Ion Exchange; D016384:Consensus Sequence; D003432:Cross-Linking Reagents / Q000494:pharmacology; D019281:Dimerization; D004587:Electrophoresis, Agar Gel; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D015603:Keratinocytes; D007633:Keratins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011233:Precipitin Tests; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D003432:Cross-Linking Reagents; D011994:Recombinant Proteins; D007633:Keratins