The Source Organism browser is a hierarchical representation of all organisms in the NCBI Taxonomy database. Only organisms that are the source of naturally-occurring polymers (proteins and nucleic acids) whose structures are in the PDB are listed as active links in the browser. The PDB source organism assignment is based on author/UniProtKB specified mapping of polypeptides.
Here you can browse protein entities by source organism, and then search for the specific associated structures.