The NCBI Related Structures tool allows you to find 3D structures from the Molecular Modeling Database (MMDB) that are similar in sequence to a query protein. Although the query protein may not yet have a resolved structure, the 3D shape of a similar protein sequence can shed light on the putative shape and biological function of the query protein.

• This page allows you to enter the sequence identifier of any record already in the Entrez Protein database.
• By default, precalculated search results will be presented. Each sequence in the Entrez Protein database is compared against all protein sequences that have 3D structures as part of standard data processing at NCBI. The results of these "precalculated" searches are stored and updated each time new 3D structures are added to MMDB.
• If a live search is preferred, use the BLAST page to do a protein-protein (blastp) query against the Protein Data Bank proteins (pdb)
• To find related structures for a query sequence that is not currently in the Entrez Protein database, enter the query sequence in FASTA format on the live BLAST page noted above.