The role of side chain conformational flexibility in surface recognition by Tenebrio molitor antifreeze protein.
Two-dimensional nuclear magnetic resonance spectroscopy was used to investigate the flexibility of the threonine side chains in the beta-helical Tenebrio molitor antifreeze protein (TmAFP) at low temperatures. From measurement of the (3)J(alphabeta) (1)H-(1)H scalar coupling constants, the chi(1) angles and preferred rotamer populations can be calculated. It was determined that the threonines on the ice-binding face of the protein adopt a preferred rotameric conformation at near freezing temperatures, whereas the threonines not on the ice-binding face sample many rotameric states. This suggests that TmAFP maintains a preformed ice-binding conformation in solution, wherein the rigid array of threonines that form the AFP-ice interface matches the ice crystal lattice. A key factor in binding to the ice surface and inhibition of ice crystal growth appears to be the close surface-to-surface complementarity between the AFP and crystalline ice, and the lack of an entropic penalty associated with freezing out motions in a flexible ligand.
Daley
Margaret E
ME
Canadian Institutes of Health Research (CIHR) Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
Sykes
Brian D
BD
D000595:Amino Acid Sequence; D000818:Animals; D021301:Antifreeze Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008969:Molecular Sequence Data; D018583:Pliability; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry; D012995:Solubility; D013696:Temperature; D013712:Tenebrio / Q000737:chemistry*; D013912:Threonine / Q000737:chemistry
D021301:Antifreeze Proteins; D020033:Protein Isoforms; D013912:Threonine