Cause (5/5)

Anchoring fibrils

Type VII collagen is the primary component of anchoring fibrils. Type VII collagen contains a large N-terminal globular domain (NC-1), which interacts with laminin 5 in the lamina densa; a long collagenous domain; and a smaller C-terminal globular domain (NC-2), which is cleaved proteolytically during anchoring fibril formation. Type VII collagen chains form a triple helix and 2 molecules join together in an antiparallel fashion in the next step. Next, anchoring fibrils are formed by lateral associations of antiparallel dimers. Anchoring fibrils wind around the dermal interstitial collagen fibrils and reinsert back upon the lamina densa, attaching the BMZ to the underlying dermis.

Cause (4/5)

Anchoring filaments

These structures contain the extracellular portions of collagen XVII (BP180) and alpha-6-beta-4 (α-6-β-4) integrin. In addition, anchoring filaments contain the molecules ‘laminin 5’ and ‘laminin 6’. Similar to all members of the family of laminin proteins, laminin 5 is a large heterotrimeric molecule, containing α-3, β-3, and g-2 chains. Laminin 5 forms a disulfide-bonded attachment to laminin 6, the other known anchoring filament laminin, which contains α-3, β-1, and g-1 chains. Laminin 5 also forms a strong association with type VII collagen, which serves to connect anchoring filaments with anchoring fibrils.

Cause (3/5)

Hemidesmosomes

The structure of ‘Hemidesmosomes’ contain intracellular proteins including ‘plectin’ and ‘BP230’.

Plectin (HD1) is a 500-kd protein which binds intermediate filaments.

BP230 (also termed as BPAG1) is a 230-kd protein which has homology to both desmoplakin and plectin. BP230, like plectin, functions in the connection between ‘hemidesmosomes’ and ‘intermediate filaments’.

Hemidesmosomes also contain the intracellular portions of the transmembrane proteins collagen XVII (BP180) and alpha-6-beta-4 (α-6-β-4) integrin. The β-4 integrin subunit performs a central role in hemidesmosome formation and contains an especially large cytoplasmic domain, which interacts with other proteins of the hemidesmosomal plaque. Collagen XVII is a transmembrane collagenous protein which interacts with α-4 integrin and BP230 intracellularly and with laminin 5 extracellularly.