Pertaya Natalya, Marshall Christopher B, Celik Yeliz, Davies Peter L, Braslavsky Ido
Department of Physics and Astronomy, Ohio University, Athens, Ohio, USA.
Biophys J. 2008 Jul;95(1):333-41. doi: 10.1529/biophysj.107.125328. Epub 2008 Mar 13.
Antifreeze proteins (AFPs) protect certain organisms from freezing by adhering to ice crystals, thereby preventing their growth. All AFPs depress the nonequilibrium freezing temperature below the melting point; however AFPs from overwintering insects, such as the spruce budworm (sbw) are 10-100 times more effective than most fish AFPs. It has been proposed that the exceptional activity of these AFPs depends on their ability to prevent ice growth at the basal plane. To test the hypothesis that the hyperactivity of sbwAFP results from direct affinity to the basal plane, we fluorescently tagged sbwAFP and visualized it on the surface of ice crystals using fluorescence microscopy. SbwAFP accumulated at the six prism plane corners and the two basal planes of hexagonal ice crystals. In contrast, fluorescently tagged fish type III AFP did not adhere to the basal planes of a single-crystal ice hemisphere. When ice crystals were grown in the presence of a mixture of type III AFP and sbwAFP, a hybrid crystal shape was produced with sbwAFP bound to the basal planes of truncated bipyramidal crystals. These observations are consistent with the blockage of c-axial growth of ice as a result of direct interaction of sbwAFP with the basal planes.
抗冻蛋白（AFPs）通过附着在冰晶上保护某些生物免受冻害，从而阻止冰晶生长。所有抗冻蛋白都会将非平衡冻结温度降低到熔点以下；然而，来自越冬昆虫（如云杉芽虫，sbw）的抗冻蛋白比大多数鱼类抗冻蛋白的效果要高10到100倍。有人提出，这些抗冻蛋白的特殊活性取决于它们阻止冰在基面生长的能力。为了验证sbwAFP的高活性源于其与基面的直接亲和力这一假设，我们对sbwAFP进行荧光标记，并使用荧光显微镜在冰晶表面观察它。sbwAFP聚集在六棱柱平面的角上以及六方冰晶的两个基面上。相比之下，荧光标记的III型鱼类抗冻蛋白没有附着在单晶冰半球的基面上。当在III型抗冻蛋白和sbwAFP的混合物存在的情况下使冰晶生长时，会产生一种混合晶体形状，其中sbwAFP结合在截顶双锥体晶体的基面上。这些观察结果与sbwAFP与基面的直接相互作用导致冰的c轴生长受阻一致。
