Antifreeze proteins (AFP) afford protection for organisms from freezing damage due to their function to inhibit the growth of seed-ice crystals. In biomedical research, AFPs find applications in cold protection of mammalian cells, tissues and organs, and in enhancement of tumor cell destruction for cryosurgery. For example, experiments demonstrated that AFPs could help protect biological functions of whole rat livers following hypothermic cryogenic storage, which has significant impact on improving the quality and shelf time for human organ transplantations. Although the structures and function of AFPs have been extensively studied, the precise mechanism of antifreeze action is still not fully understood. The long-term goal of this research is to find the antifreeze mechanism and to develop an antifreeze theory for the purpose of finding particular antifreeze materials and designing sophisticated antifreeze methods for the subsequent biomedical research and applications. To understand the antifreeze mechanism, this research will test the following hypotheses: (1) AFPs tend to diffuse to the water-ice interface to form a water-AFP-ice (WAI) interfacial region due to the decrease in Gibbs energy, and the ice growth inhibition arises primarily from the colligative effect of the enhanced interfacial AFP concentration;(2) the structural match of AFPs with ice surfaces and the van der Waals interactions of AFPs'hydrophobic side chains with ice surfaces are the most important driving forces for AFPs to tend to stay in the WAI interfacial region, and the interactions of AFPs'hydrophilic side chains with liquid water enhance the solubility and also balance the their interacting sides with ice surfaces. The following complementary approaches will be carried out for this study: (1) We will continue to develop thermodynamic theoretical model and perform experimental approaches, including volumetric and thermal analyses of Gibbs energy, enthalpy and entropy changes, to understand AFPs'antifreeze action. (2) We will continue the study in the direction of probing structural interactions and dynamics of type I AFPs in the WAI interfacial region via using specific side-chain NMR-active isotope-labeled AFPs, and developing and applying cutting-edge NMR techniques including double resonance NMR and spin lattice relaxation NMR. (3) Molecular modeling will be carried out to understand the functional roles of specific residues of type I AFPs with the input of the experimentally determined structural and dynamic data.
| Ba, Yong; Mao, Yougang; Galdino, Luiz et al. (2013) Effects of a type I antifreeze protein (AFP) on the melting of frozen AFP and AFP+solute aqueous solutions studied by NMR microimaging experiment. J Biol Phys 39:131-44 |
| Mao, Yougang; Jeong, Myongho; Wang, Tieli et al. (2011) Threonine side chain conformational population distribution of a type I antifreeze protein on interacting with ice surface studied via ýýýýC-ýýýýýN dynamic REDOR NMR. Solid State Nucl Magn Reson 39:7-13 |
