Study on molecular co-evolution of enzyme and substrate

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In previous phylogenetic analysis, we suggested that fishes included in Elopomorpha, as basal teleosts, possess a single type of hatching enzyme genes, and that fishes in Otocephala and Euteleostei gain two types of hatching enzyme genes called clade I and II genes by duplication. The Elopomorph hatching enzyme and the clade I enzyme swell the egg envelope by cleaving the N-terminal regions of ZP proteins, while the clade II enzyme solubilizes the swollen envelope by cleaving the two specific sites at N-terminal of ZP domain and the middle region on the ZP domain. In the evolutionary scenario, our findings support that the clade I enzymes inherit the ancestral enzyme function, and the clade II enzymes gain a new function during evolution to Otocephala and Euteleostei. Our study also suggested that a change in the egg envelope protein during evolution strongly contributed to the acquisition of a new function of euteleostean clade II enzyme.