Graduate School of Life Science, Hokkaido University, Sapporo 060-0810, Japan.
Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Sapporo 062-8517, Japan.
Biomolecules. 2020 Mar 9;10(3):423. doi: 10.3390/biom10030423.
The concentration of a protein is highly related to its biochemical properties, and is a key determinant for its biotechnological applications. Antifreeze proteins (AFPs) and antifreeze glycoproteins (AFGPs) are structurally diverse macromolecules that are capable of binding to embryonic ice crystals below 0 °C, making them useful as protectants of ice-block formation. In this study, we examined the maximal solubility of native AFP I-III and AFGP with distilled water, and evaluated concentration dependence of their ice-binding property. Approximately 400 mg/mL (AFP I), 200 mg/mL (AFP II), 100 mg/mL (AFP III), and >1800 mg/mL (AFGP) of the maximal solubility were estimated, and among them AFGP's solubility is much higher compared with that of ordinary proteins, such as serum albumin (~500 mg/mL). The samples also exhibited unexpectedly high thermal hysteresis values (2-3 °C) at 50-200 mg/mL. Furthermore, the analysis of fluorescence-based ice plane affinity showed that AFP II binds to multiple ice planes in a concentration-dependent manner, for which an oligomerization mechanism was hypothesized. The difference of concentration dependence between AFPs and AFGPs may provide a new clue to help us understand the ice-binding function of these proteins.
蛋白质的浓度与其生化特性高度相关，是其生物技术应用的关键决定因素。抗冻蛋白 (AFPs) 和抗冻糖蛋白 (AFGPs) 是结构多样的大分子，能够在 0°C 以下与冰晶结合，使其成为防止冰晶形成的保护剂。在这项研究中，我们检查了天然 AFP I-III 和 AFGP 与蒸馏水的最大溶解度，并评估了它们结合冰的特性的浓度依赖性。估计 AFP I 的最大溶解度约为 400 mg/mL，AFP II 为 200 mg/mL，AFP III 为 100 mg/mL，AFGP 为 >1800 mg/mL，与普通蛋白质（如血清白蛋白，约 500 mg/mL）相比，AFGP 的溶解度要高得多。这些样品在 50-200 mg/mL 时还表现出出人意料的高热滞值（2-3°C）。此外，基于荧光的冰面亲和力分析表明，AFP II 以浓度依赖的方式与多个冰面结合，推测存在一个寡聚化机制。AFPs 和 AFGPs 之间的浓度依赖性差异可能为我们理解这些蛋白质的冰结合功能提供新的线索。
