Adsorption-induced conformational changes of antifreeze glycoproteins at the ice/water interface.
The conformation of antifreeze glycoprotein (AFGP) molecules adsorbed at the ice/water interface was studied by attenuated total reflection (ATR)-FTIR spectroscopy. Measurements were carried out for AFGP/D2O solution films formed on the surface of an ATR prism as a function of temperature. Using the FTIR spectrum from the O-D stretching band of D2O molecules, we monitored the supercooled and frozen states of the film and measured the thickness of the quasi-liquid layer (QLL) at the ice/prism interfaces. The AFGP structure was determined for the liquid, supercooled, and frozen states of the solution film using the amide I band spectra. No noticeable differences in conformation were observed in the solution conformation from room temperature down to the 15 K supercooling studied, whereas the alpha-helical content of AFGP suddenly increased when the supercooled solution film froze at -15 degrees C. This change in conformation can increase the overall interaction between the AFGP molecules and ice surface and allow a stronger adsorption. In contrast, the alpha-helical content of AFGP in the frozen film gradually decreased with increasing temperature and finally returned to its solution-state level at the melting point of D2O ice. This gradual decrease in the alpha-helix content directly correlates with the measured increase in QLL thickness. Finally, we conclude that the differences in the alpha-helix signals between the frozen and supercooled states indicate the conformational change of AFGP molecules upon adsorption at the ice/water interface, emphasizing the importance of the structure-function relationship, even for this highly flexible antifreeze.
Uda
Yukihiro
Y
Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo 060-0819, Japan.
Zepeda
Salvador
S
Kaneko
Fumitoshi
F
Matsuura
Yoshiki
Y
Furukawa
Yoshinori
Y
D000327:Adsorption; D021301:Antifreeze Proteins / Q000737:chemistry*; D017666:Deuterium Oxide / Q000737:chemistry; D007053:Ice; D008968:Molecular Conformation; D044367:Phase Transition; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D014867:Water / Q000737:chemistry*
D021301:Antifreeze Proteins; D007053:Ice; D014867:Water; D017666:Deuterium Oxide