Metacaspases are members of the C14 class of cysteine proteases and thus related to caspases, orthocaspases and paracaspases. The metacaspases are Arginine/Lysine-specific, in contrast to caspases, which are Aspartate-specific.
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Prokaryotes
In archea and bacteria, there are several metacaspases with a wide range of domain organizations. Based on the prokaryote metacaspase diversity, paracaspases and orthocaspases can be considered sub-classes among the metacaspases. Common for all three classes are 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.
Eukaryotes
Metacaspases are found in plants, fungi, and "protists", but not in slime mold or animals.
Type I
Type I metacaspases are characterized by an amino-terminal proline or glutamine rich LSD zinc finger-like domain. This class can almost exclusively be found in plants, with one recent exception where both type I and type II metacaspases were found in the genome of Monosiga brevicollis (Choanoflagellate), possibly as a result of an unusual horizontal gene transfer between two eukaryotes.
Type II
Type II has a wider phylogenetic distribution among all eukaryotes except those where paracaspases have been found (animals and slime mold). This group is characterized by lacking an amino-terminal domain.
Known functions
In an analogous manner to caspases, metacaspases induce programmed cell death in both plants and fungi (yeast).