Paracaspase

The "type 2" paracaspases in animals represent the ancestral form which only consists of a caspase-like domain. This form of paracaspase can be found in ctenophora, trichoplax, sponges and cnidarians. Cnidarians also have "type 1" paracaspases.[3]

Species key: Hs= Human, Gg = Chicken, Xt = African clawed frog, Dr = Zebrafish, Cm = Elephant Shark, Pm = Lamprey, Bf = Lancelet, Sk = Acorn worm, Cg = Pacific oyster, Ob = Octopus, Dp = Daphnia, Am = Honey bee, Ce = nematode, Nv = Nematostella, Hv = Hydra.

The "type 1" paracaspases are characterized by a MALT1-like domain composition with a death domain, immunoglobulin-like domains and a caspase-like domain. The "type 1" paracaspases first originated sometime before the last common ancestor of the bilaterans and cnidaria, indicating that "type 1" paracaspases originated during the ediacaran period.[3] The jawed vertebrates (starting from sharks) have 3 paralogs: PCASP1, PCASP2 and PCASP3. PCASP3 is the ancestral copy and can be found in all deuterostomes, like sea urchin, lancelets, tunicates and lampreys (a non-jawed vertebrate). Notably, mammals have lost PCASP2 and PCASP3 and only have PCASP1 (MALT1).[3] The non-deuterostome invertebrate type 1 paracaspase closest related to PCASP3 can surprisingly be found in molluscs, which could indicate that there were 2 paralog type 1 paracaspases present in the first bilaterans (like in cnidarians), and that different bilateran lineages have kept one or the other paralog.[4]

The paracaspase in Dictyostelium seems to regulate osmotic stress tolerance by vacuolar expansion.[5]

Paracaspase in animals has mostly been studied in humans and mice (see: MALT1), where it plays a major role in several pro-inflammatory pathways in innate- and adaptive- immunity. The distantly related zebrafish PCASP3 show conserved MALT1-like activity in NF-kappaB activation and protease substrate specificity, indicating that these functions were present in the last common ancestor of the three vertebrate paracaspase paralogs.[3]