Electro-Optical Properties Characterization of Fish Type III Antifreeze Protein

Abstract

Antifreeze proteins (AFPs) are ice-binding proteins that depress the freezing point of water in a non-colligative manner without a significant modification of the melting point. Found in the blood and tissues of some organisms (such as fish, insects, plants, and soil bacteria), AFPs play an important role in subzero temperature survival. Fish Type III AFP is present in members of the subclass Zoarcoidei. AFPIII are small 7-kDa-or 14-kDa tandem-globular proteins. In the present work, we study the behavior of several physical properties, such as the low-frequency dielectric permittivity spectrum, circular dichroism, and electrical conductivity of Fish Type III AFP solutions measured at different concentrations. The combination of the information obtained from these measurements could be explained through the formation of AFP molecular aggregates or, alternatively, by the existence of some other type of interparticle interactions. Thermal stability and electrooptical behavior, when proteins are dissolved in deuterated water, were also investigated.

Low thermodynamic but high kinetic stability of an antifreeze protein from Rhagium mordax

“…The T m of RmAFP1 at pH 7.4 was determined by CD spectroscopy to be 28.5 C. This method is widely used for this purpose, 20,21,[25][26][27][28] and has the advantage over DSC that it circumvents the question of heating rate. With DSC the T mApp was calculated to be 45.1 C at 1 C/min.…”

“…By extrapolating the k 2 values obtained at [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] C to the T m at 28.5 C (R 2 5 0.981, exponential regression) we obtain a k 2 and k 1 of 0.00526 min…”

“…A high refolding capacity has also been observed for other AFPs. 13,[19][20][21][22] In two cases the activity of the protein was measured to ensure that the protein refolded to its native state, and only one of these showed that the protein (DAFP-4) had retained most of its activity. Here, we also show that the RmAFP1 has activity almost similar to the untreated control after subjection to 10 heat cycles to both 60 and 70 C. When the protein sample was repeatedly heated to 80 C the DH unfold decreased by 6.5% of the initial value per run (Fig.…”

“…Thus, the protein is thermodynamically quite heat labile and has a remarkably low T m of 28.5 C at pH 7.4. The transitions between folded and unfolded states are slow, and show apparent negative activation energy of refolding in the studied temperature interval of [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] C, which may reflect temperature dependent changes in the folding pathway. In contrast to the marginal thermodynamic stability, the protein shows a conspicuous colloidal stability, as the majority of the activity is regained after repeated heat cycles up to 70 C, that is, virtually all protein returns to the folded state following cooling.…”

Neutron structure of type‐III antifreeze protein allows the reconstruction of AFP–ice interface

“…The synthetic gene of the type-III AFP corresponding to the sequence of the 1HG7 PDB entry (http://www.rcsb.org/pdb/ explore/explore.do?structureId¼1HG7) (Antson et al, 2001) was used (Salvay et al, 2007). It was over-expressed in Escherichia coli BL21(DE3) at the ILL-EMBL Deuteration Facility in Grenoble, France (Petit-Haertlein et al, 2009).…”