The CYP3 clan includes a large group of CYP families, starting with CYP6 an CYP9 and now numbering at least 160 families in arthropods. The CYP3 clan sequences are most closely related to vertebrate CYP3 and CYP5 families. The human CYP3A4 crystal structure is the closest known structure of a CYP3 clan P450. Because of the initial “lumping” of Papilio polyxenes CYP6B1 with the original house fly CYP6A1 into the CYP6 family and later “splitting” of the CYP300s, this group is rather heterogeneous with regard to names of CYP families and subfamilies.
Many CYP3 clan enzymes have been characterized (table) and in many, but not all, studies they are shown to metabolize xenobiotics and plant natural compounds. Genes from this group appear to share the characteristics of “environmental response genes” as defined by Berenbaum (2002), specifically (1) very high diversity, (2) proliferation by duplication events, (3) rapid rates of evolution, (4) occurrence in gene clusters, and (5) tissue- or temporal-specific expression. Of course these characteristics are not independent of each other, they are difficult to measure objectively, and they are not exclusive to the CYP3 clan.