Type XVII collagen (BP180) and LAD-1 are present as separate trimeric complexes

This study characterized the high molecular mass BP180 complex that is obse rved when unheated sodium dodecyl sulfate extracts of human skin or keratin ocytes are subjected to sodium dodecyl sulfate-polyacrylamide gel electroph oresis and immunoblotting. In heated extracts BP180 is present as a monomer with a molecular weight of 180 kDa, in unheated extracts BP180 runs at a m olecular weight position over 500 kDa, By preincubating the unheated extrac ts at temperatures between 31 degrees C and 40 degrees C, the high molecula r weight complex could be "melted" down to monomeric BP180. Under the condi tions employed the T-1/2 Of the dissociation process was between 35 degrees C and 36 degrees C. The temperature resistance of the high molecular weigh t complex was used to analyze its molecular composition by performing two-d imensional electrophoresis with a "low-temperature" first dimension step an d a "high-temperature" second dimension step. Silver staining and immunoblo tting of the two-dimensional gels revealed the high molecular weight comple x to be composed of solely BP180, indicating that the complex is the nondis sociated homotrimeric form of BP180. The 120 kDa linear IgA dermatosis anti gen (LAD-1) is an collagenous anchoring filament protein with homology to t he extracellular collagenous part of BP180, Two-dimensional immunoblotting showed that LAD-1, as BP180, is also present as a high molecular mass compl ex and does not form mixed complexes with BP180.