SEQUENCE-ANALYSIS OF THE GOODPASTURE ANTIGEN OF MAMMALS

Background. Autoimmunity to the NCl domain of the alpha 3 chain of typ e IV collagen (alpha 3(IV)NCl), the Goodpasture antigen, is the cause of spontaneous human antiglomerular basement membrane (anti-GBM) disea se, and of anti-GBM nephritis in several animal models. Methods. We ha ve derived amino acid sequences from alpha 3(IV)NCl for a number of ma mmalian species (monkey, sheep, pig, dog, rabbit, and rat) by RT-PCR a nd cDNA cloning. The GBM of some species was studied comparatively for binding to Goodpasture autoantibodies. Results. From this work and ot her data the sequences of nine mammalian species can be aligned. Regio ns and residues that may be functionally important are identified. alp ha 3(IV)NCl sequences were found to be less closely conserved across s pecies than alpha 1 and alpha 2(IV)NCl, 91 to 99% in comparison to a m inimum of 97% for alpha 1, but these differences were unevenly distrib uted along the molecule. There was a particularly striking homology be tween rodent and human sequences in the carboxyl-terminal region. Bind ing of Goodpasture autoantibodies to rat alpha 3(IV)NCl was poor in co mparison with other species. Conclusions. Comparison of sequences and binding casts doubt on the importance of the carboxyl-terminal region for antibody binding, a region identified as a potential major epitope in previous studies. Sequence comparisons suggest possible reasons fo r the nephritogenicity of alpha 3(IV)NCl in active models of anti-GBM disease.