Hyperactive antifreeze protein from fish contains multiple ice-binding sites.
Antifreeze proteins (AFPs) are produced to prevent freezing in many fish species that are exposed to icy seawater. There are a number of nonhomologous types of AFPs, diverse in both sequence and structure, which share the function of binding to ice and inhibiting its growth. We recently discovered a hyperactive AFP in the winter flounder and related species that is many-fold more active than other fish AFPs. Like the 3-4-kDa type I AFPs, it is alanine-rich and highly helical, but this 17-kDa protein is considerably larger and forms a dimer. We have sequenced the cDNA encoding this new AFP to gain insight into its structure and evolutionary relationship to the type I AFP family. The gene is clearly homologous to the righteye flounder type I AFP genes. Thus we have designated this protein "hyperactive type I AFP" (hyp-type I). The sequence of hyp-type I AFP supports a structural model in which two extended 195-amino acid alpha-helices form an amphipathic homodimer with a series of linked Ala- and Thr-rich patches on the surface of the dimer, each of which resembles ice-binding sites of type I AFPs. The superior activity of hyp-type I AFP may derive from the large combined surface area of the ice-binding sites, recognition of multiple planes of ice, and protection of the basal plane from ice growth.
Graham
Laurie A
LA
Department of Biochemistry and Protein Function Discovery Group, Queen's University, Kingston, Ontario, Canada K7L 3N6.
Marshall
Christopher B
CB
Lin
Feng-Hsu
FH
Campbell
Robert L
RL
Davies
Peter L
PL
D000595:Amino Acid Sequence; D000818:Animals; D021301:Antifreeze Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D017931:DNA Primers; D018076:DNA, Complementary; D005432:Flounder; D007053:Ice; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D021301:Antifreeze Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D007053:Ice