Conformational diversity of the Goodpasture antigen, the noncollagenous-1 domain of the α3 chain of collagen IV

The noncollagenous-1 domain of the alpha 3 chain of collagen IV networks of basement membranes is the target of an antibody-mediated inflammatory response in Goodpasture autoimmune disease. This domain when excised from basement membranes by bacterial collagenase digestion exists in two molecular forms, M-H and M-L, that differ in cleavage site and mobility in SDS-PAGE. In the present study, M-H and M-L were shown to also differ with respect to epitope exposure, susceptibility to endoprotease digestion, and redox states of specific cystene residues, as determined by MS. Moreover, M-H and M-L assemble to form different quaternary structures, critically influencing pathogenic epitope(s) exposure and autoantibody binding. Collectively, our findings reveal that M-H and M-L are conformational isomers stabilized by a distinct disulfide bond connectivity, and coexist in basement membranes. The hitherto unrecognized conformational diversification of the Goodpasture autoantigen may be of relevance in pathogenesis.