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Hyperactive antifreeze protein from an A ntarctic sea ice bacterium C olwellia sp. has a compound ice‐binding site without repetitive sequences
Author(s) -
Hanada Yuichi,
Nishimiya Yoshiyuki,
Miura Ai,
Tsuda Sakae,
Kondo Hidemasa
Publication year - 2014
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.12878
Subject(s) - antifreeze protein , psychrophile , ice crystals , antifreeze , chemistry , freezing point , crystallography , biochemistry , binding site , biophysics , biology , organic chemistry , physics , optics , thermodynamics , enzyme
Antifreeze proteins (AFPs) are structurally diverse macromolecules that bind to ice crystals and inhibit their growth to protect the organism from injuries caused by freezing. An AFP identified from the Antarctic bacterium Colwellia sp. strain SLW05 ( Col AFP) is homologous to AFPs from a wide variety of psychrophilic microorganisms. To understand the antifreeze function of Col AFP, we have characterized its antifreeze activity and determined the crystal structure of this protein. The recombinant Col AFP exhibited thermal hysteresis activity of approximately 4 °C at a concentration of 0.14 m m , and induced rapid growth of ice crystals in the hexagonal direction. Fluorescence‐based ice plane affinity analysis showed that Col AFP binds to multiple planes of ice, including the basal plane. These observations show that Col AFP is a hyperactive AFP. The crystal structure of Col AFP determined at 1.6 Å resolution revealed an irregular β‐helical structure, similar to known homologs. Mutational and molecular docking studies showed that Col AFP binds to ice through a compound ice‐binding site (IBS) located at a flat surface of the β‐helix and the adjoining loop region. The IBS of Col AFP lacks the repetitive sequences that are characteristic of hyperactive AFPs. These results suggest that Col AFP exerts antifreeze activity through a compound IBS that differs from the characteristic IBSs shared by other hyperactive AFPs. This study demonstrates a novel method for protection from freezing by AFPs in psychrophilic microorganisms. Database Structural data for Col AFP have been submitted to the Protein Data Bank (PDB) under accession number 3WP9 .