Purification and Characterization of？Antifreeze Protein from the Arctic Bacterium Aquaspirillum sp. KOPRI-AB30

Abstract

Antifreeze proteins (AFPs), a.k.a. ice-structuring proteins (ICPs), inhibit the growth of ice crystals by binding to the surface of ice crystals via hydrogen-bond. They also show inhibition of ice recrystallization. We isolated bacteria capable of producing antifreeze proteins as part of cold adaptation mechanism from the Arctic. Of these, the strain KOPRI-AB30 showed high antifreeze activity and was identified as Aquaspirillum sp. The psychrophilic arctic bacterium, Aquaspirillum sp. KOPRI-AB30, produced antifreeze protein extracellularly. The optimal temperature and pH for the production of AFP were 5℃ and 7.0, respectively. The AFP was purified from the culture supernatant using modified cold-finger method. The ice-crystal controlling activity of the AFP was observed using nanaoliter osmometer. Molecular weight of the purified AFP was approximately 20 kDa. Peptide mapping analysis showed that this protein shares sequence similarity to Ice-binding proteins from certain algae and fungi. The thermal hysteresis of the protein was determined to be about 0.7℃. In addition, the AFP is relatively heat and pH stable, but not calcium dependant. The inhibition of ice recrystallization was also determined.