Evolution of keratin genes: Different protein domains evolve by different pathways

Abstract

Intermediate filaments are composed of a family of proteins that evolved from a common ancestor. The proteins consist of three domains: a central, alpha-helical domain similar in all intermediate filaments, bracketed by two domains that are variable in length and structure. Within the intermediate-filament family, several subfamilies have been recognized by immunologic and nucleic acid hybridization techniques. In this paper we present the sequence of the genomic DNA coding for a 65-kilodalton human keratin and compare it with the sequences of other intermediate-filament proteins. While the central, alpha-helical domains of these proteins show homologies that indicate a common ancestor, the sequences of the variable terminal domains indicate that the variable domains evolved through a series of tandem duplications and possibly by gene-conversion mechanisms.

Few Simple Sequence Repeats in Human Hair

“…This may be achieved by elongation of repeats leading to longer amino acid repeats thus, modifying the protein 97 . Most introns in hair keratin genes begin with 5' GT and end with 3' AG nucleotide combination which is similar to observations of study on keratin Type II gene 13 .…”

“…This is in agreement with earlier studies on keratin genes that show similarity in sequences, exon/intron structure including Type I hair keratin genes 8 and conserved elements in promoter region 10 . Analyses of introns in most eukaryotic genes also confirm conservation of positions of introns 13,[91][92][93] . The present study shows partial concurrence with the study that suggests higher intronic burden in evolutionarily conserved genes 94 .…”

“…Study of structural organization of exons/introns in cytoplasmic IF protein genes shows homologous position of many introns; indicating common ancestry of lamins and IF proteins 13,90 . Variations and conservations of introns in lamin genes indicate linage specificity 90 .…”

“…The exception is hHb4 gene with nine introns which is in the 3' noncoding region 12 . Moreover, most introns in Type II keratin genes begin with 5' GT and end with 3' AG nucleotide combination 13 . Many disorders are associated with mutations in human keratin genes [14][15][16][17] .…”

Unique amino acid signatures that are evolutionarily conserved distinguish simple-type, epidermal and hair keratins

“…Accordingly, the rod domain has probably evolved from a common ancestor through conservative substitutions and a deletion of a six heptad subdomain, whereas the terminal domains have probably arisen through tandem duplications. Consequently, when compared on an inter-species basis, the chains tend to exhibit conservation in length rather than in primary structure (Klinge et al, 1987).…”