What is HSSP curve?
HSSP is a derived database merging structural (3-D) and sequence (1-D) information. For each protein of known 3-D structure from the Protein Data Bank (PDB), the database has a multiple sequence alignment of all available homologues and a sequence profile characteristic of the family. The list of homologues is the result of a database search in SwissProt using a position-weighted dynamic programming method for sequence profile alignment (MaxHom). The database is updated frequently. The listed homologues are very likely to have the same 3-D structure as the PDB protein to which they have been aligned. As a result, the database is not only a database of aligned sequence families, but also a database of implied secondary and tertiary structures covering 29% of all SwissProt-stored sequences.
References: http://en.wikipedia.org/wiki/Homology-derived_Secondary_Structure_of_Proteins http://www.ncbi.nlm.nih.gov/pubmed/?term=UniqueProt%3A+creating+representative+protein+sequence+sets http://en.wikipedia.org/wiki/Protein_superfamily