The DSSP algorithm (Kabsch & Sander, Biopolymers. [1983] 22:2577-2637) annotates the secondary structure of protein structures in detail, including hydrogen bonding and beta sheet topology. The DSSP databank provides these annotations for all structure models in the Protein Data Bank (PDB). The annotations are available in two formats: annotated mmCIF files (preferred) and the DSSP format (deprecated).