title: Systematic size study of an insect antifreeze protein and its interaction with ice.
abstract: Because of their remarkable ability to depress the freezing point of aqueous solutions, antifreeze proteins (AFPs) play a critical role in helping many organisms survive subzero temperatures. The beta-helical insect AFP structures solved to date, consisting of multiple repeating circular loops or coils, are perhaps the most regular protein structures discovered thus far. Taking an exceptional advantage of the unusually high structural regularity of insect AFPs, we have employed both semiempirical and quantum mechanics computational approaches to systematically investigate the relationship between the number of AFP coils and the AFP-ice interaction energy, an indicator of antifreeze activity. We generated a series of AFP models with varying numbers of 12-residue coils (sequence TCTxSxxCxxAx) and calculated their interaction energies with ice. Using several independent computational methods, we found that the AFP-ice interaction energy increased as the number of coils increased, until an upper bound was reached. The increase of interaction energy was significant for each of the first five coils, and there was a clear synergism that gradually diminished and even decreased with further increase of the number of coils. Our results are in excellent agreement with the recently reported experimental observations.
authors.affiliation: Department of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China.
authors.forename: Kai
authors.initials: K
authors.lastname: Liu
authors.forename: Zongchao
authors.initials: Z
authors.lastname: Jia
authors.forename: Guangju
authors.initials: G
authors.lastname: Chen
authors.forename: Chenho
authors.initials: C
authors.lastname: Tung
authors.forename: Ruozhuang
authors.initials: R
authors.lastname: Liu
mesh_terms: D000818:Animals; D021301:Antifreeze Proteins / Q000032:analysis / Q000737:chemistry* / Q000648:ultrastructure*; D001665:Binding Sites; D003198:Computer Simulation; D019281:Dimerization; D004735:Energy Transfer; D007053:Ice; D046911:Macromolecular Substances / Q000032:analysis / Q000737:chemistry; D008958:Models, Molecular; D008970:Molecular Weight; D046912:Multiprotein Complexes / Q000032:analysis / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D011789:Quantum Theory; D013329:Structure-Activity Relationship; D013712:Tenebrio / Q000378:metabolism; D014867:Water / Q000032:analysis / Q000737:chemistry*
chemical_list: D021301:Antifreeze Proteins; D007053:Ice; D046911:Macromolecular Substances; D046912:Multiprotein Complexes; D014867:Water