Cryo-EM structure of ex vivo fibrils associated with extreme AA amyloidosis prevalence in a cat shelter

We present the 3.3 Å cryo-EM structure of an AA amyloid extracted post-mortem from the diseased kidney of a DSH cat with renal failure. The structure reveals a cross-beta architecture assembled from two 76-residue long proto-filaments. Despite >70% sequence homology to mouse and human SAA, the cat SAA variant adopts a unique amyloid fold exhibiting type-2 polymorphism. Based on shared disease profiles and almost identical sequences, we propose a similar amyloid fold of deposits identified previously in captive cheetah.