title: Structure and evolutionary origin of Ca(2+)-dependent herring type II antifreeze protein.
abstract: In order to survive under extremely cold environments, many organisms produce antifreeze proteins (AFPs). AFPs inhibit the growth of ice crystals and protect organisms from freezing damage. Fish AFPs can be classified into five distinct types based on their structures. Here we report the structure of herring AFP (hAFP), a Ca(2+)-dependent fish type II AFP. It exhibits a fold similar to the C-type (Ca(2+)-dependent) lectins with unique ice-binding features. The 1.7 A crystal structure of hAFP with bound Ca(2+) and site-directed mutagenesis reveal an ice-binding site consisting of Thr96, Thr98 and Ca(2+)-coordinating residues Asp94 and Glu99, which initiate hAFP adsorption onto the [10-10] prism plane of the ice lattice. The hAFP-ice interaction is further strengthened by the bound Ca(2+) through the coordination with a water molecule of the ice lattice. This Ca(2+)-coordinated ice-binding mechanism is distinct from previously proposed mechanisms for other AFPs. However, phylogenetic analysis suggests that all type II AFPs evolved from the common ancestor and developed different ice-binding modes. We clarify the evolutionary relationship of type II AFPs to sugar-binding lectins.
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore, Singapore.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Zhengjun
authors.initials: Z
authors.lastname: Li
authors.forename: Qingsong
authors.initials: Q
authors.lastname: Lin
authors.forename: Jan
authors.initials: J
authors.lastname: Kosinski
authors.forename: J
authors.initials: J
authors.lastname: Seetharaman
authors.forename: Janusz M
authors.initials: JM
authors.lastname: Bujnicki
authors.forename: J
authors.initials: J
authors.lastname: Sivaraman
authors.forename: Choy-Leong
authors.initials: CL
authors.lastname: Hew
mesh_terms: D000818:Animals; D021341:Antifreeze Proteins, Type II / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D003460:Crystallization; D018360:Crystallography, X-Ray; D019143:Evolution, Molecular; D005399:Fishes / Q000235:genetics* / Q000378:metabolism; D037102:Lectins / Q000378:metabolism; D008958:Models, Molecular; D010802:Phylogeny; D011485:Protein Binding; D011487:Protein Conformation; D013329:Structure-Activity Relationship
chemical_list: D021341:Antifreeze Proteins, Type II; D037102:Lectins; D002118:Calcium