Structure of the N-terminal didomain d1_d2 of the Thrombospondin type-1 domain-containing 7A
Thrombospondin type-1 domain-containing 7A (THSD7A) is a large extracellular protein that is found in podocyte foot processes of the kidney glomerulus. It has been established as a causative autoantigen in membranous nephropathy. Amongst the predicted 21 thrombospondin repeat domains of its extracellular segment, the highest frequency of autoimmune response has been associated with the two N-terminal domains. Here, we show that antibodies against this THSD7A segment in mice induce typical clinical and morphological signs of membranous nephropathy. The high-resolution structure of these two domains reveals a non-canonical thrombospondin repeat fold that is distinct from the established type 1 thrombospondin repeat. As it shares a conserved disulfide pattern with the canonical fold, we refer to these domains d1 and d2 as type 1A thrombospondin repeats. Both domains comprise a seven layered CC-W-PP-R-W-QQ-CC pattern, which is only partly shared by other THSD7A thrombospondin repeat domains. The two domains form a well-defined V-shaped tandem arrangement. Our findings provide crucial insight into specific structural features of these two domains that are distinct from other regions of THSD7A and hence could cause the high level of antigenicity found for these two domains.