Dominant-Negative Keratin Variant in a Filament Assembly Domain
trigger
A heterozygous missense or small in-frame insertion/deletion variant falls in a keratin domain required for filament assembly - characteristically a helix boundary motif at the start of the 1A or the end of the 2B rod segment, or the H1 head domain. These are the regions that mediate the end-to-end molecular overlaps between adjacent keratin molecules, so a substitution there yields a chain that still enters the filament but cannot support normal assembly.
Used by disorders
Monilethrix
as Dominant-Negative Hair Cortex Keratin Variant
Downstream
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Keratin Filament Network Collapse and Aggregation
The mutant chain is incorporated into the obligate heterodimer and disrupts assembly of the whole network in trans.
Show evidence (2 references)
"Moreover, analyses of all mutations in epidermolytic hyperkeratosis known to date demonstrate remarkable clustering in the molecular overlap region."
Establishes that pathogenic keratin variants cluster in the assembly domains mediating molecular overlap, which is the claim of this node.
"Dominant-negative mutations in any of the four identified keratin genes, KRT6A, KRT6B, KRT16, or KRT17, cause pachyonychia congenita (PC), characterized by hypertrophic nail dystrophy and other ectodermal features."
Documents the dominant-negative mode of action in a second keratin pair and a second tissue, supporting the mechanism as shared rather than gene-specific.
Keratin Filament Network Collapse and Aggregation
amplifier
Because keratin filaments are obligate heterodimers of a type I and a type II chain, mutant protein from a single allele is incorporated throughout the network rather than segregating from it. The filament system fails to form a normal cytoplasmic array and instead collapses into perinuclear clumps and tonofilament aggregates - the ultrastructural hallmark of this disease group, and the basis of the clumped tonofilaments seen in Dowling-Meara EBS.
Downstream
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Loss of Keratinocyte Mechanical Resilience
A collapsed filament network no longer distributes mechanical load across the cell.
Show evidence (2 references)
"we engineered one of these point mutations in a cloned human K14 cDNA, and showed that a K14 with an Arg-125----Cys mutation disrupted keratin network formation in transfected keratinocytes and perturbed filament assembly in vitro"
Directly demonstrates the trigger-to-amplifier step: a patient point mutation, reintroduced experimentally, disrupts keratin network formation.
"As predicted for a dominant-negative disease, simultaneous expression of both wild-type and mutant K6a resulted in defective keratin filament formation. Addition of mutant-specific siRNAs allowed normal filament formation, suggesting selective inhibition of mutant K6a."
Shows the dominant-negative logic explicitly - wild-type protein does not rescue, and removing only the mutant transcript restores the network.
Loss of Keratinocyte Mechanical Resilience
central effector
The keratin network is the load-bearing element of the keratinocyte, so its collapse leaves the cell unable to withstand shear and compression. This is the rate-limiting, disorder-agnostic node of the module: every affected keratin pair converges here, and conformance should be declared against it.
Used by disorders
Monilethrix
as Defective Keratin Assembly in the Hair Shaft Cortex
Downstream
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Keratinocyte Cytolysis Within the Keratin Expression Domain
Mechanically incompetent cells rupture, and they do so in whichever epithelial layer or appendage expresses the affected keratin pair.
Show evidence (2 references)
"These data indicate that abnormalities of either of the components of the keratin intermediate filament heterodipolymer can impair the mechanical stability of these epithelial cells."
States this node directly, and states it for either chain of the heterodimer, which is why the module is keratin-pair-agnostic.
"The disorder results from a mutation in either the keratin 5 or keratin 14 gene, which encode the peptide components of the obligate heterodimeric keratin intermediate filaments of the basal cell."
Confirms the obligate-heterodimer architecture that makes a single mutant allele sufficient to compromise resilience.
Keratinocyte Cytolysis Within the Keratin Expression Domain
effector
Cells lyse under mechanical stress, producing a plane of tissue disruption at the level where the affected keratin pair is expressed. This node is where the module's single mechanism becomes several distinct diseases: basal K5/K14 cytolysis splits the epidermis at its base and blisters; suprabasal K1/K10 cytolysis produces the vacuolar degeneration of epidermolytic ichthyosis; K6/K16/K17 involvement affects nail bed, palmoplantar epidermis and pilosebaceous units; hair-cortex keratins produce a fragile, beaded hair shaft.
Downstream
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Mechanically Provoked Blistering, Hyperkeratosis and Appendage Dystrophy
Repeated cytolysis in the affected compartment produces the clinical phenotype characteristic of that keratin pair.
Show evidence (2 references)
"Epidermolysis bullosa simplex (EBS) is characterized by skin blistering due to basal keratinocyte fragility."
Documents the basal-layer instance of this node, produced by the K5/K14 pair.
"Mutations in keratins K5 or K14 are found in epidermolysis bullosa simplex."
Anchors the basal expression domain to its disease; the same source maps the suprabasal K1/K10 pair to epidermolytic hyperkeratosis, which is the expression-domain principle this node asserts.
Mechanically Provoked Blistering, Hyperkeratosis and Appendage Dystrophy
consequence
The clinical endpoint, which varies with the expression domain but is uniformly provoked or worsened by friction and pressure: trauma-induced blistering favouring hands and feet; erythema and blistering in the neonate giving way to thick adherent hyperkeratosis; focal palmoplantar keratoderma with disabling plantar pain and hypertrophic nail dystrophy; or fragile beaded hair with patchy alopecia. Because the trigger is mechanical, disease burden tracks physical activity and heat, and management is largely protective.
Show evidence (2 references)
"This inherited keratinization disorder is characterized clinically by erythema, blistering, and peeling shortly after birth. It may resolve and be replaced with thick scaling."
Documents the suprabasal K1/K10 endpoint, in which neonatal blistering is succeeded by hyperkeratosis.
"The Weber-Cockayne subtype of epidermolysis bullosa simplex is an inherited skin-fragility disorder characterized by basal keratinocyte lysis and epidermal blistering confined primarily to the hands and feet."
Documents the basal K5/K14 endpoint and its localization to the most mechanically stressed sites, which is the module's mechanical logic.