@dugu9sword You probably shouldn't call the results of cryo-EM "density maps" - that phrase can be used in casual conversation, but is not appropriate for a publication.
@Nature because he saw in solving the structure of hemoglobin the resemblance to myoglobin. He reasoned that if this was the case for these structures, it is likely for others too and to deny previous structures to aid elucidation of new ones would set the field back decades.
@Nature Helen Berman didn't dream up a database. The PDB was started in 1971 by Walter Hamilton and team. Helen Berman became the director of the PDB in 1998 - 27 years later. It was Max Perutz who first pushed for a public archive of protein structures...