A method for the isolation of the NC1 domain of
type IV collagen has been developed using the EHS
sarcoma, a basement membrane-producing mouse
tumor. This NC1 domain has been compared to the NC1 of human glomerular basement membrane (hGBM) to assess its usefulness in the biochemical characterization of the
Goodpasture antigen which is associated with NC1. Both NC1 isolates appeared to migrate by gel filtration as hexamers (Mr 160,000) and in SDS-
polyacrylamide gel electrophoresis as dimers and monomers (Mr 54,000 and 26,000), and were shown to share biochemical identity by
amino acid analysis. The hGBM NC1 showed greater complexity in the monomer region, and when compared by two-dimensional gel electrophoresis was found to contain more components in both regions than EHS NC1.
Anti-GBM autoantibodies from patients with
Goodpasture's syndrome reacted with the EHS NC1 by immunoblotting of two-dimensional
gels. The EHS NC1 isolated by reverse phase HPLC partially inhibited the reactivity of the
anti-GBM autoantibodies against hGBM NC1 by inhibition ELISA assay. Reverse phase HPLC elution of EHS and hGBM NC1 showed differences in subunit composition and interaction; complete dissociation of the EHS monomers and dimers in 0.1%
trifluoroacetic acid was observed, whereas hGBM monomers and dimers eluted together. Rotary shadowing of hGBM NC1 domains revealed size heterogeneity of globular domains, compared with greater uniformity of EHS NC1 hexamers. We conclude that EHS NC1 contains an
epitope(s) that is reactive with human
autoantibodies to hGBM NC1. However, the immune response in
Goodpasture's syndrome may involve
antibodies directed against
epitopes which are present in greater density and on a more complex array of
peptides in the hGBM NC1 than in EHS NC1.