I'm trying to find examples of crystal structures where "cross-species" interactions are being represented. A few examples are 2R03, 3DCG, 1ZLA. My thought was to parse the PDB files and find instances where the "Source" of each polymer is different. I know this will produce plenty of false-positives but it should hopefully be good against false-negatives.
The problem I'm having is that I can't find the "Source" information in any of the downloadable file formats (in the ftp-data directory).
Does anyone know where this information is stored? I would prefer not to resort to HTML scraping of the search page ... but I will if needed.