title: Structure and dynamics of a beta-helical antifreeze protein.
abstract: Antifreeze proteins (AFPs) protect many types of organisms from damage caused by freezing. They do this by binding to the ice surface, which causes inhibition of ice crystal growth. However, the molecular mechanism of ice binding leading to growth inhibition is not well understood. In this paper, we present the solution structure and backbone NMR relaxation data of the antifreeze protein from the yellow mealworm beetle Tenebrio molitor (TmAFP) to study the dynamics in the context of structure. The full (15)N relaxation analysis was completed at two magnetic field strengths, 500 and 600 MHz, as well as at two temperatures, 30 and 5 degrees C, to measure the dynamic changes that occur in the protein backbone at different temperatures. TmAFP is a small, highly disulfide-bonded, right-handed parallel beta-helix consisting of seven tandemly repeated 12-amino acid loops. The backbone relaxation data displays a periodic pattern, which reflects both the 12-amino acid structural repeat and the highly anisotropic nature of the protein. Analysis of the (15)N relaxation parameters shows that TmAFP is a well-defined, rigid structure, and the extracted parameters show that there is similar restricted internal mobility throughout the protein backbone at both temperatures studied. We conclude that the hydrophobic, rigid binding site may reduce the entropic penalty for the binding of the protein to ice. The beta-helical fold of the protein provides this rigidity, as it does not appear to be a consequence of cooling toward a physiologically relevant temperature.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
authors.forename: Margaret E
authors.initials: ME
authors.lastname: Daley
authors.forename: Leo
authors.initials: L
authors.lastname: Spyracopoulos
authors.forename: Zongchao
authors.initials: Z
authors.lastname: Jia
authors.forename: Peter L
authors.initials: PL
authors.lastname: Davies
authors.forename: Brian D
authors.initials: BD
authors.lastname: Sykes
mesh_terms: D000818:Animals; D016880:Anisotropy; D021301:Antifreeze Proteins / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D019476:Insect Proteins / Q000737:chemistry*; D008958:Models, Molecular; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012996:Solutions; D013712:Tenebrio / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D021301:Antifreeze Proteins; D019476:Insect Proteins; D009587:Nitrogen Isotopes; D012996:Solutions