Identification and expression of an elastase homologue in Branchiostoma belcheri with implications to the origin of vertebrate pancreas.

Elastases have been identified in a variety of organisms ranging from bacteria to insects to mammals, yet little is known to date about them in amphioxus, a model animal for insights into the origin and evolution of vertebrates. In this study we demonstrate the presence of an elastase homologue, named BbElas, in Branchiostoma belcheri. The recombinant BbElas hydrolyses the elastase specific substrate N-succinyl-Ala-Ala-Ala p-nitroanilide, which can be inhibited by the serine proteinase inhibitor PMSF, the elastase-specific inhibitor elastatinal and the cysteine proteinase inhibitor PCMB. Phylogenetic analysis shows that BbElas represents the archetype of vertebrate elastases, hinting at the clues that the different isoforms of vertebrate elastases are originated from an ancestral gene like BbElas. Our results also suggest that the mid-gut in amphioxus is to homologous vertebrate pancreas, a novel proposal which deserves further study.