Collagen XVII is a transmembrane protein. It is a structural component of hemidesmosomes, multiprotein complexes at the dermal-epidermal basement membrane zone that mediate adhesion of keratinocytes to the underlying membrane. Two homotrimeric forms exist; a full length transmembrane form and a soluble form, referred to as either ectodomain or LAD-1, which is generated by proteolytic processing of the full length form by TACE (TNF-Alpha Converting Enzyme), a metalloproteinase of the ADAM family (fRANZKE ET AL. 2004). Each alpha-chain has an intracellular domain which interacts with beta4-integrin (Hopkinson et al. 1998), plectin and dystonin (BP230) and is necessary for the stable attachment of hemidesmosomes to keratin intermediate filaments (Hopkinson & Jones 2000).