An intracellular antifreeze protein from an Antarctic microalga that responds to various environmental stresses

The structure and function of the Antarctic marine diatom Chaetoceros neogracile antifreeze protein (Cn‐AFP), as well as its expression levels and characteristics of the ice‐binding site, were analyzed in the present study. In silico analysis revealed that the Cn‐AFP promoter contains both light‐ and temperature‐responsive elements. Northern and Western blot analyses demonstrated that both Cn‐AFP transcript and protein expression were strongly and rapidly stimulated by freezing, as well as temperature and high light stress. Immunogold labeling revealed that Cn‐AFP is preferentially localized to the intracellular space near the chloroplast membrane. Recombinant Cn‐AFP had clear antifreeze activity. Protein‐folding simulation was used to predict the putative ice‐binding sites in Cn‐AFP, and site‐directed mutagenesis of the Cn‐AFP b‐face confirmed their identification.—Gwak, Y., Jung, W., Lee, Y., Kim, J. S., Kim, C. G., Ju, J.‐H., Song, C., Hyun, J.‐K., Jin, E. An intracellular antifreeze protein from an Antarctic microalga that responds to various environmental stresses. FASEB J. 28, 4924–4935 (2014). www.fasebj.org