ATP2A2 and glycogen storage disease VI: However, because there was no registered 3D structure of SPCA1 in the Protein Data Bank, which is the basis for the 3D structure analysis software Waals (Altif Labs, Inc), we used the structure of human SERCA2 (Darier disease-causing protein), which shares the highest homology with SPCA1, for the 3D structure model.5