Extensive size polymorphism of the human keratin 10 chain resides in the C-terminal V2 subdomain due to variable numbers and sizes of glycine loops.

Abstract

Existing data suggest that the human keratin 10 intermediate filament protein is polymorphic in amino acid sequence and in size. To precisely define the nature of the polymorphism, we have used PCR amplification and sequence analyses on DNA from several individuals including five with documented size variations of the keratin 10 protein. We found no variation in the N-terminal or rod domain sequences. However, we observed many variations in the V2 subdomain near the C terminus in glycine-rich sequences with a variation of as much as 114 base pairs (38 amino acids), but all individuals had either one or two variants. Our results show that (i) the keratin 10 system is far more polymorphic than previously realized, (is) the polymorphism is restricted to insertions and deletions of the glycine-rich quasipeptide repeats that form the glycine-loop motif in the C-terminal domain, (iii) the polymorphism can be accounted for by simple allelic variations that segregate by normal Mendelian mechanisms, and (iv) the differently sized PCR products most likely represent different alleles of a single-copy gene per haploid genome.Keratins form a large family of cytoplasmic intermediate filaments (IFs). The more than 30 known keratin chains are differentially expressed along the different pathways of epithelial cell development and differentiation. They are subdivided into acidic type I and neural-basic type II chains. Most epithelial cells express a particular pair of type I and type II chains that assemble into keratin IFs characteristic of that cell type (1-6). For example, terminally differentiating epidermal keratinocytes express keratins 1 (type II) and 10 (K1O; type I).Keratins, like all other IF proteins, have a central a-helical rod domain of conserved secondary structure. The rod domain is flanked on both sides by end domains that display particular patterns that permit their classification into subdomains. These subdomains are the high homology or H subdomains, regions with sequence variation or V subdomains, and highly charged ends or E subdomains (1, 2, 7). For K10, the rod domain is flanked on the N-terminal end by El, Vi, and H1 subdomains and on the C-terminal side by V2 and E2 subdomains (Fig. 1).-Although the principles of the structural organization of the rod domain and its possible function during IF assembly are largely known (9-11), little is known about the structure and function of the end domains of the IFs. In comparison to most other keratins, the E and V subdomains of epidermal keratins 1 and 10 are unusually glycine-rich (8,(12)(13)(14) and, therefore, likely to adopt a distinct configuration and conceivably possess a unique function (15). Notably, solid-state NMR experiments have

Against the Rules: Human Keratin K80

“…15, and references therein). Anatomical regions particularly exposed to wear and tear, such as the sole of the foot or the palms of the hand, express additional keratins of this type.…”

“…Anatomical regions particularly exposed to wear and tear, such as the sole of the foot or the palms of the hand, express additional keratins of this type. Their glycine-rich sequences have been shown to form highly flexible loop configurations that are thought to be responsible for cellular plasticity and resilience of the epithelium (15,30). As these glycine-rich loops are not present in the K80 molecule, the function of the keratin must lie elsewhere.…”

A functional "knockout" of human keratin 14.

“…The subdomains VI (in the head domain) and V2 (in the tail domain) of keratins consist largely of glycinerich crude repeats and, therefore, the DNA sequences encoding these domains are potential targets for dele tion-insertion mutations. In-frame insertional polymor phism of the VI and V2 subdomains of a number of ker atins has been described (Korge et al 1992a(Korge et al , 1992b) and produces no known pathology. As seen here, a frameshift deletion in the VI domain can produce a functionally 2568 …”

Overexpression of human loricrin in transgenic mice produces a normal phenotype.

“…novel glycine loop motif which is variable in sequence and highly flexible in likely conformation (16,17). Since the same glycine loop motifexists on the keratin intermediate filaments also expressed in terminally differentiated epithelial cells (16,(18)(19)(20), it was proposed that an interaction between the glycine loop sequences of loricrin on the CE and on the intracellular keratin intermediate filaments may stabilize cellular structure (16).…”