title: Isolation and characterization of type I antifreeze proteins from cunner, Tautogolabrus adspersus, order Perciformes.
abstract: Antifreeze proteins (AFPs) are produced by many species of teleost fish that inhabit potentially lethal ice-laden seawater and afford them protection from freezing. To date type I AFPs have been fully characterized in two teleost orders: Pleuronectiformes and Scorpaeniformes. In this study, we report the isolation and complete characterization of a type I AFP present in fish from a third order: cunner (Tautogolabrus adspersus), order Perciformes (family Labridae). This protein was purified from blood plasma and found to belong to what is now known as classical type I AFP with their small size (mass 4095.16 Da), alanine richness (> 57 mol%), high α-helicity (> 99%) with the ability to undergo reversible thermal denaturation, 11 amino acid (ThrX(10)) repeat regions within the primary structure, the capacity to impart a hexagonal bipyramidal shaping to ice crystals and the conservation of an ice-binding site found in many of the other type I AFPs. Partial de novo sequencing of the plasma AFP accounted for approximately half of the peptide mass. Sequencing of a combined liver and skin cDNA library indicated that the protein is produced without a signal sequence. In addition the translated product of the AFP cDNA suggests that it codes for the AFP isolated from plasma. These results further solidify the hypothesis that type I AFPs are multiphyletic in origin and suggest that they represent remarkable examples of convergent evolution within three orders of teleost fish.
authors.affiliation: Ocean Sciences Centre, Memorial University of Newfoundland, St John's, NL, Canada.
authors.forename: Rod S
authors.initials: RS
authors.lastname: Hobbs
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Shears
authors.forename: Laurie A
authors.initials: LA
authors.lastname: Graham
authors.forename: Peter L
authors.initials: PL
authors.lastname: Davies
authors.forename: Garth L
authors.initials: GL
authors.lastname: Fletcher
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D021322:Antifreeze Proteins, Type I / Q000097:blood* / Q000737:chemistry / Q000235:genetics; D001483:Base Sequence; D018076:DNA, Complementary / Q000032:analysis; D007053:Ice / Q000032:analysis; D008969:Molecular Sequence Data; D010473:Perciformes / Q000097:blood* / Q000502:physiology; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D012621:Seasons; D016415:Sequence Alignment; D053719:Tandem Mass Spectrometry
chemical_list: D021322:Antifreeze Proteins, Type I; D018076:DNA, Complementary; D007053:Ice