Crystal structures of the wild type and A20V-mutant for the anti freeze protein AFP6 derived from Japanese fish Zoarces elongatus Kner

Adachi, Motoyasu; Ohara, Takashi   ; Nishimiya, Yoshiyuki*; Kondo, Hidemasa*; Shimizu, Rumi; Tamada, Taro; Tsuda, Sakae*; Kuroki, Ryota

Antifreeze proteins can interfere with growing of ice and are focused from the viewpoint of the basic principles and practical applications in science and technology. Previously, it was found that most of the mutant nfeAFP6s showed similar activity to that of the wild type nfeAFP6 whereas A20V-mutant nfeAFP6 showed strong anti-freezing activity. In this study, crystal structures of the wild type and the A20V-mutant AFPs were determined to 1.2 and 1.8 resolution, respectively, by X-ray crystallography to investigate the difference of hydration structure around the essential area. The side chain of Val20 in A20V-mutant faces to the side chain Gln9, and make van der Waals interactions with Gln9 and Thr18. We found the locations of some bound water molecules at the mutated region in A20V-mutant were different from those in wild type. These observations may illustrate the complexity of what hydration structure constitutes to an ice-binding and anti-freezing activity.