Antifreeze Glycoprotein Activity Correlates with Long-Range Protein-Water Dynamics
ABSTRACT Antifreeze proteins (AFPs) and antifreeze glycoproteins (AFGPs) enable the survival of organisms living in subfreezing habitats and serve as preservatives. Although their function is known, the underlying molecular mechanism was not understood. Mutagenesis experiments questioned the previous assumption of hydrogen bonding as the dominant mechanism. We use terahertz spectroscopy to show that antifreeze activity is directly correlated with long-range collective hydration dynamics. Our results provide evidence for a new model of how AFGPs prevent water from freezing. We suggest that antifreeze activity may be induced because the AFGP perturbs the aqueous solvent over long distances. Retarded water dynamics in the large hydration shell does not favor freezing. The complexation of the carbohydrate cis-hydroxyl groups by borate suppresses the long-range hydration shell detected by terahertz absorption. The hydration dynamics shift toward bulk water behavior strongly reduces the AFGP antifreeze activity, further supporting our model.
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ABSTRACT: This study reports on structural characteristics of hyperactive antifreeze proteins (AFPs) from two species of longhorn beetles. In Rhagium mordax, eight unique mRNAs coding for five different mature AFPs were identified from cold-hardy individuals. These AFPs are apparently homologues to a previously characterized AFP from the closely related species Rhagium inquisitor, and consist of six identifiable repeats of a putative ice binding motif TxTxTxT spaced irregularly apart by segments varying in length from 13 to 20 residues. Circular dichroism spectra show that the AFPs from both species have a high content of β-sheet and low levels of α-helix and random coil. Theoretical predictions of residue-specific secondary structure locate these β-sheets within the putative ice-binding motifs and the central parts of the segments separating them, consistent with an overall β-helical structure with the ice-binding motifs stacked in a β-sheet on one side of the coil. Molecular dynamics models based on these findings show that these AFPs would be energetically stable in a β-helical conformation.Journal of insect physiology 11/2012; 58(11):1502–1510. DOI:10.1016/j.jinsphys.2012.09.004 · 2.50 Impact Factor
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ABSTRACT: We examine dynamics of water molecules and hydrogen bonds at the water-protein interface of the wild-type antifreeze protein from spruce budworm Choristoneura fumiferana and a mutant that is not antifreeze active by all-atom molecular dynamics simulations. Water dynamics in the hydration layer around the protein is analyzed by calculation of velocity autocorrelation functions and their power spectra, and hydrogen bond time correlation functions are calculated for hydrogen bonds between water molecules and the protein. Both water and hydrogen bond dynamics from subpicosecond to hundred picosecond time scales are sensitive to location on the protein surface and appear correlated with protein function. In particular, hydrogen bond lifetimes are longest for water molecules hydrogen bonded to the ice-binding plane of the wild type, whereas hydrogen bond lifetimes between water and protein atoms on all three planes are similar for the mutant.Journal of Atomic Molecular and Optical Physics 03/2012; 6(1687-9228). DOI:10.1155/2012/125071
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ABSTRACT: THz-Spektroskopie ist eine neue experimentelle Methode, um kleinste Änderungen der kollektiven schnellen Wassernetzwerkdynamik an der Biomolekül-Wasser-Grenzfläche zu detektieren. Die Resultate unterstreichen die Bedeutung des Wassers für die biologische Funktion. THz spectroscopy is a new experimental tool to detect even small soluteinduced changes of the collective water network dynamics at the biomolecule-water interface. The new results underline the role of water for the biological function.BioSpektrum 01/2011; 17(1):38-41. DOI:10.1007/s12268-011-0008-4