ABSTRACT
In this paper, we report our study of thermodynamic parameters of the interactions of antifreeze proteins (AFP) type I and it short segments with DMPC unilamellar vesicles as model for cell membrane. The heat of interactions between AFP's and the model cell membrane were studied by Isothermal Titration Calorimetry (ITC) at temperatures above and below phase transition temperatures of the membrane. It is shown that heat of interactions is linearly dependent on the temperatures below the phase transition of the membrane and constant at temperatures above phase. The heat of interaction above phase transition is assigned to the interaction of the AFP with the membrane, while below phase transition the ordering effect of the AFP influence the heat of interaction.
Subject(s)
Antifreeze Proteins, Type I/chemistry , Calorimetry/methods , Dimyristoylphosphatidylcholine/chemistry , Lipid Bilayers/chemistry , Antifreeze Proteins, Type I/metabolism , Cell Membrane/chemistry , Cell Membrane/metabolism , Dimyristoylphosphatidylcholine/metabolism , Lipid Bilayers/metabolism , Phase Transition , Protein Binding , Temperature , Thermodynamics , Time Factors , Transition Temperature , Unilamellar Liposomes/chemistry , Unilamellar Liposomes/metabolismABSTRACT
In this paper, we report on the effect of short segments of type I antifreeze protein (AFP I) on the thermotropic properties of a model membrane. Two different types of dimyristoylphosphatidylcholine model membranes were used, multilamellar vesicles and small unilamellar vesicles. The membrane properties were studied by differential scanning calorimetry (DSC) and fluorescence anisotropy. With the incorporation of AFP I and its short segments, the order of the model membrane increased both in the gel state and in the liquid crystalline state. The interaction of AFPs with the model membrane caused a shift in the phase transition to lower temperatures, which is accompanied by a broadening of the DSC thermogram. This preferential stabilization to a more ordered phase by the AFPs could be due to ordering the hydrophobic membrane core and separation into domains. Overall, this approach of employing short segments of AFP I simplifies the correlation between antifreeze protein characteristics and the effect of these parameters on the interaction mechanism of AFP with cell membranes. The success of this approach can lead to the identification of short peptides with high antifreeze activity.
Subject(s)
Antifreeze Proteins/chemistry , Lipid Bilayers/chemistry , Membrane Fluidity , Unilamellar Liposomes/chemistry , TemperatureABSTRACT
In this work, we present a study on the antifreeze activity of short segments of a Type I antifreeze protein, instead of the whole protein. This approach simplifies the correlation between antifreeze protein characteristics, such as hydrophilicity/hydrophobicity, and the effect of these characteristics on the antifreeze mechanism. Three short polypeptides of Type I AFP have been synthesized. Their antifreeze activity and interactions with water and ice crystals have been analyzed by various techniques such as circular dichroism spectroscopy, X-ray diffraction, differential scanning calorimetry, and osmometry. It is shown that one short segment of Type I AFP has an antifreeze activity of about 60% of the native protein activity. In this work, we demonstrate that short segments of Type I AFPs possess nonzero thermal hysteresis and result in modifications in the growth habits and growth rates of ice. This approach enables the preparation of large quantities of short AFP segments at low cost with high antifreeze activity, and opens the possibility of developing the commercial potential of AFPs.
