{{tag>structure}}

===== Homologous Superfamily =====

This level of the CATH hierarchy groups together protein domains which are thought to share a common ancestor and can therefore be described as homologous. Similarities are identified either by high sequence identity or structure comparison using [[glossary:ssap | SSAP]]. Structures are clustered into the same homologous superfamily if they satisfy two or more of the following criteria:

    * Sequence identity >= 35%, overlap >= 60% of larger structure equivalent to smaller.
    * SSAP score >= 80.0, sequence identity >= 20%, overlap 60% of larger structure equivalent to smaller.
    * SSAP score >= 70.0, overlap 60% of larger structure equivalent to smaller; domains which have related functions, which is informed by the literature and Pfam protein family database.
    * Significant similarity from HMM-sequence searches and HMM-HMM comparisons using SAM, HMMER (http://hmmer.wustl.edu) and PRC (http://supfam.org/PRC).


===== References =====

{{pubmed>long:14681378}}
{{pubmed>long:8744772}}