A
protein superfamily is the largest grouping (
clade) of proteins for which
common ancestry can be inferred (see
homology). Usually this common ancestry is based on
structural alignment and mechanistic similarity even though no sequence similarity is evident. Superfamilies typically contain several
protein families which show sequence similarity within the family. The term
protein clan is commonly used for
protease superfamilies based on the
MEROPS protease classification system.