Psoriasis is a chronic inflammatory skin disease. The absence of microbial
organisms as potential causal agents has given rise to the hypothesis that the
inflammation is due to an autoimmune reaction. The defined inflamed areas of the
skin lesions argue for an immunological disease with a local production of a
causal antigen. Pso p27 is a protein generated in mast cells in psoriatic
plaques, but not in uninvolved skin. We recently demonstrated that the Pso p27
is generated by cleavage of SerpinB3 (SCCA1) in the presence of mast cell
associated chymase. In this communication we demonstrate by X-ray
crystallographic analysis that the cleavage products associate into a complex
similar to SCCA1, but with the reactive centre loop inserted into a 5-stranded
central β-sheet. Native gel electrophoresis show that these Pso p27 complexes
form large aggregates which may be of significance with respect to an
immunogenic role of Pso p27.
