Substructure Searching in the PDB: Tableau
Tableau allows for the searching of protein folding patterns of substructures in the PDB structural database. This type of searching can be helpful in understanding protein structure, function and evolution.
The server searches using secondary structure elements and is capable of finding either an entire structure or a substructure of a larger structure (ref).
Tableau has a number of simple inputs (title, email, desired structure, output), however, you want to read the suggested tips. You can submit structures that contain multiple chains or domains, but it is not recommended. I submitted a number of structures and had a response time of about 3 minutes.
The server is also handy for tracking down fake structures.
