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Crystal structure of antifreeze protein from an Antarctic sea ice bacterium Colwellia sp.
Structural highlights
FunctionIBP_COLSX Binds to the surface of ice crystals and inhibits their growth (PubMed:17651136, PubMed:24938370). Has ice recrystallization inhibition (RI) activity (the ability to prevent the formation of larger grains of ice at the expense of smaller grains), which may protect membranes from freezing injury (Probable). Has high thermal hysteresis (TH) activity, which is the ability to lower the freezing point of an aqueous solution below its melting point, and thus the freezing of the cell fluid can be prevented protecting the organism from ice damage. The TH activity of this protein is 3.8 degrees Celsius at 14 mM (PubMed:24938370).[1] [2] [3] Publication Abstract from PubMedAntifreeze proteins (AFPs) are structurally diverse macromolecules that bind to ice crystals and inhibit their growth to protect organism from injuries caused by freezing. An AFP identified from an Antarctic bacterium, Colwellia sp. strain SLW05 (ColAFP) is homologous to AFPs from a wide variety of psychrophilic microorganisms. To understand the antifreeze function of ColAFP, we have characterized the antifreeze activity and determined the crystal structure of this protein. The recombinant ColAFP exhibited thermal hysteresis activity of approximately 4 degrees C at a concentration of 0.14 mM and induced a rapid growth of ice crystals in the hexagonal direction. Fluorescence-based ice plane affinity analysis showed that ColAFP binds to multiple planes of ice including the basal plane. These observations classify ColAFP as a hyperactive AFP. The crystal structure of ColAFP determined at 1.6-A resolution revealed an irregular beta-helical structure, which is similar to known homologs. Mutational and molecular docking studies clarified that ColAFP binds to ice through a compound ice-binding site (IBS) located at a flat surface of the beta-helix and the adjoining loop region. The IBS of ColAFP lacks repetitive sequences which has been recognized as a characteristic of hyperactive AFPs. These results conclude that ColAFP exerts antifreeze activity by utilizing its compound IBS, which is distinct from the characteristic feature of IBS shared by other hyperactive AFPs. This study represents a novel aspect for protection from freezing achieved by AFPs in psychrophilic microorganisms. This article is protected by copyright. All rights reserved. Hyperactive antifreeze protein from an Antarctic sea ice bacterium Colwellia sp. has a compound ice-binding site without repetitive sequences.,Hanada Y, Nishimiya Y, Miura A, Tsuda S, Kondo H FEBS J. 2014 Jun 17. doi: 10.1111/febs.12878. PMID:24938370[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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