BPAG2

BPAG2, also known as BP180 or type XVII collagen, is a transmembrane collagen component of hemidesmosomes that anchors basal keratinocytes to the basement membrane. It is a major autoantigen in bullous pemphigoid and is encoded by the COL17A1 gene.

BP180 is a single-pass transmembrane glycoprotein composed of an extracellular large collagenous region with a non-collagenous NC16A domain near the membrane, a transmembrane segment, and a short cytoplasmic tail. The extracellular portion mediates adhesion to the basement membrane, while the cytoplasmic domain interacts with intracellular hemidesmosomal proteins such as BP230 and plectin, linking to the keratin cytoskeleton.

In basal keratinocytes, BP180 contributes to the stability of hemidesmosomes that attach the epidermis to the dermis, working in concert with laminins and type IV collagen in the basement membrane to maintain skin integrity.

Clinical significance of BPAG2 centers on its role as an autoantigen in bullous pemphigoid. Autoantibodies directed against BP180, particularly the NC16A region, can disrupt hemidesmosomes and promote blister formation. Diagnosis often involves detecting anti-BP180 antibodies and observing linear IgG and C3 deposition along the basement membrane by immunofluorescence. Mutations in COL17A1 can cause inherited skin fragility disorders characterized by epidermal detachment in certain contexts.