The MeSH browser organizes PDB structures by a hierarchical set of keywords applied to publication that describe PDB structures. The majority of PDB structures have associated a primary citation that is listed on the Structure Summary page. That citation includes an abstract and keywords. The MeSH (Medical Subject Headings) are the keywords or MeSH terms indexed by the National Library of Medicine (NLM) by a human annotator.
Here you can browse the MeSH tree to find all structures at a given level of the tree that have an abstract which include the selected MeSH term as a keyword.