MUTATIONS IN THE NON-HELICAL LINKER SEGMENT L1-2 OF KERATIN-5 IN PATIENTS WITH WEBER-COCKAYNE EPIDERMOLYSIS-BULLOSA SIMPLEX

Keratins are the major structural proteins of the epidermis. Analyzing keratin gene sequences, appreciating the switch in keratin gene expre ssion that takes place as epidermal cells commit to terminally differe ntiate, and elucidating how keratins assemble into 10 nm filaments, ha ve provided the foundation that has led to the discoveries of the gene tic bases of two major classes of human skin diseases, epidermolysis b ullosa simplex (EBS) and epidermolytic hyperkeratosis (EH). These dise ases involve point mutations in either the basal epidermal keratin pai r, K5 and K14 (EBS), or the suprabasal pair, K1 and K10 CEH). In sever e cases of EBS and EH, mutations are found in the highly conserved end s of the alpha-helical rod domain, regions that, by random mutagenesis , had already been found to be important for 10 nm filament assembly. In order to identify regions of the keratin polypeptides that might be more subtly involved in 10 nm filament assembly and to explore the di versity in mutations within milder cases of these diseases, we have fo cused on Weber-Cockayne EBS, where mild blistering occurs primarily on the hands and feet in response to mechanical stress. In this report, we show that affected members of two different W-C EBS families have p oint mutations within 1 residue of each other in the non-helical linke r segment of the K5 polypeptide. Genetic linkage analyses, the absence of this mutation in >150 wild-type alleles and filament assembly stud ies suggest that these mutations are responsible for the W-C EBS pheno type. These findings provide the best evidence to date that the non-he lical linker region in the middle of the keratin polypeptides plays a subtle but significant role in intermediate filament structure and/or intermediate filament cytoskeletal architecture.