Functional diversity of Teleost arylalkylamine N-acetyltransferase-2: is the timezyme evolution driven by habitat temperature?

Arylalkylamine N-acetyltransferase-2 (AANAT2) is the enzyme responsible for the rhythmic production of the time-keeping hormone melatonin. It plays a crucial role in the synchronization of biological functions with changes in the environment. Annual and daily fluctuations in light are known to be key environmental factors involved in such synchronization. Previous studies have demonstrated that AANAT2 activity is also markedly influenced by temperature but the mechanisms through which it impacts the enzyme activity need to be further deciphered. We investigated AANAT2 primary to tertiary structures (3D models) and kinetics in relation to temperature for a variety of Teleost species from tropical to Arctic environments. The results extend our knowledge on the catalytic mechanisms of AANAT enzymes and bring strong support to the idea that AANAT2 diversification was limited by stabilizing selection conferring to the enzyme well conserved secondary and tertiary structures. Only a few changes in amino acids appeared sufficient to induce different enzyme activity patterns. It is concluded that AANAT2 evolution is mainly driven by phylogenetic relationships although catalytic properties (enzyme turnover and substrate affinity) are also under the influence of the respective species normal habitat temperature.