The cDNA sequence of a human epidermal keratin: Divergence of sequence but conservation of structure among intermediate filament proteins

Abstract

We have determined the DNA sequence of a cloned cDNA that is complementary to the mRNA for the 50 kilodalton (kd) human epidermal keratin. This provides the first amino acid sequence for a cytoskeletal keratin. Comparison of this sequence with those of other keratins reveals an evolutionary relationship between the cytoskeletal and the microfibrillar keratins, but shows no homology to matrix or feather keratins. The 50 kd keratin shares 28%-30% homology with partial sequences of other intermediate filament proteins, which suggests that keratins may be the most distantly related members of this class of fibrous proteins. Our computer analyses predict that the 50 kd keratin contains two long alpha-helical domains separated by a cluster of helix-inhibitory residues in the middle of the protein. These findings indicate that despite major sequence divergence among intermediate filament proteins, they retain sequences compatible with secondary structural features that appear to be common to all of them.

Amino acid sequence microheterogeneities of a type I cytokeratin of Mr 51 000 from Xenopus laevis epidermis

“…This is considerably shorter than that of an mRNA encoding a type II cytokeratin of X. laevis epidermis (iMr 64000), which consists of an 3 '-untranslated region of 476 nucleotides [20]. A similar result has been reported for human cytokeratins [21,22].…”

“…This hypervariable region is located just at the end of the coiled-coil structure, similarly to that previously described for various basic cytokeratins of X. laevis [6]. Based on the homology with human 50 kDa cytokeratin [21,25] (see fig.2), this hypervariable region would be entirely located within exon 7.…”

“…The deduced full-length amino acid sequence (derived from pUF1371, pUFlOO1 and pUF454) results in fig. 1) with cytokeratin XK81 present in gastrulae of X. Iuevis [26] and human type I cytokeratin HSOK [21,25]. Asterisks were introduced to maximize homology (introducing gaps into the sequences) and bars in XK81 and H50K represent identical amino acid residues when compared with XL51.…”

Basal Cells Are a Multipotent Progenitor Capable of Renewing the Bronchial Epithelium

“…16 Mouse monoclonal K14 antibody (Clone LL002, 35) was purchased from NeoMarkers (Fremont, CA) and is specific for the highly conserved carboxy-terminal 16-amino acids of K14. 36,37 The K14 antigen was retrieved by microwave treatment in citrate buffer. Antigen-antibody complexes were detected using biotinylated rabbit antimouse IgG 3 (Zymed), and streptavidin-HRP.…”

Proteopedia entry: Coiled‐coil structure of keratins

“…Keratins have an important place in the history of the elucidation of protein structure as in 1951, Pauling et al suggested the first model for a-helix structure for wool a-keratins, in the absence of knowledge of the sequence of keratins [1]. The first sequence of a cytoskeletal keratin was determined in 1982 [2]. By analyzing the sequences of type I and type II keratins using secondary structure prediction methods Hanukoglu and Fuchs suggested a model for the structure of keratins and other intermediate filaments proteins [3].…”