In
archea and
bacteria, there are several metacaspases with a wide range of domain organizations.[3] Based on the prokaryote metacaspase diversity,
orthocaspases can be considered a sub-class of metacaspases. Common for both metacaspases and orthocaspases classes is their specificity for basic residues (
arginine or
lysine) in the P1 position. At this moment, no structural variants have been reported where the substrate specificity would change to an acidic residue (
aspartic acid), like in true
caspases.
Viral metacaspases, which may have implications in rewiring host metabolism to enhance
infection, are widespread in the ocean.[4]
Type I
Type I metacaspases are characterized by an amino-terminal
proline or
glutamine rich LSD
zinc finger-like domain.[5] This type can be found in prokaryotes and eukaryotes other than animals.
Type II
Type II is found only in certain green algae and land plants, with one recent exception where both type I and type II metacaspases were found in the genome of Monosiga brevicollis (
Choanoflagellate),[6] possibly as a result of an unusual
horizontal gene transfer between two
eukaryotes.This group is characterized by long linker region and the absence of an amino-terminal pro-domain.