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Welcome to the PICCOLO website. PICCOLO is a comprehensive database of structurally-characterized protein-protein interactions described at atomic level.

All protein structures deposited in the PDB comprising more than one polypeptide chain are considered. Contacts are identified by a two stage algorithm. The first stage involves a radial cutoff search to identify atoms on a separate polypeptide chain that are within 6.05Å. Any matching atom pairs are flagged as being "proximal" to one another.

In the second stage proximal atom pairs are annotated with any of a series of specified bond types depending on the atom types of the pair of atoms and the distance and angle between them. Information on the atom types for each residue can be found in the atom types images and the accompanying data table. The defined interaction types can be found in the Interaction types table.