Leiros H K, Willassen N P, Smalås A O
Department of Chemistry, Faculty of Science, University of Tromsø, Norway.
Extremophiles. 1999 Aug;3(3):205-19. doi: 10.1007/s007920050118.
The digestive enzyme trypsin is among the most extensively studied proteins, and its structure has been reported from a large number of organisms. This article focuses on the trypsins from vertebrates adapted to life at low temperatures. Cold-adapted organisms seem to have compensated for the reduced reaction rates at low temperatures by evolving more active and less temperature-stable enzymes. We have analyzed 27 trypsin sequences from a variety of organisms to find unique attributes for the cold-adapted trypsins, comparing trypsins from salmon, Antarctic fish, cod, and pufferfish to other vertebrate trypsins. Both the "cold" and the "warm" active trypsins have about 50 amino acids that are unique and conserved within each class. The main unique features of the cold-adapted trypsins attributable to low-temperature adaptation seem to be (1) reduced hydrophobicity and packing density of the core, mainly because of a lower (Ile + Leu)/(Ile + Leu + Val) ratio, (2) reduced stability of the C-terminal, (3) lack of one warm trypsin conserved proline residue and one proline tyrosine stacking, (4) difference in charge and flexibility of loops extending the binding pocket, and (5) different conformation of the "autolysis" loop that is likely to be involved in substrate binding.
消化酶胰蛋白酶是研究最为广泛的蛋白质之一，其结构已在大量生物体中被报道。本文聚焦于适应低温环境生存的脊椎动物的胰蛋白酶。适应寒冷的生物体似乎通过进化出更具活性且热稳定性更低的酶来弥补低温下反应速率的降低。我们分析了来自多种生物体的27个胰蛋白酶序列，以寻找适应寒冷的胰蛋白酶的独特特性，将鲑鱼、南极鱼类、鳕鱼和河豚的胰蛋白酶与其他脊椎动物的胰蛋白酶进行比较。“冷适应”和“温适应”活性胰蛋白酶在各自类别中均有大约50个独特且保守的氨基酸。适应低温的胰蛋白酶的主要独特特征似乎包括：（1）核心区域的疏水性和堆积密度降低，主要是因为（异亮氨酸 + 亮氨酸）/（异亮氨酸 + 亮氨酸 + 缬氨酸）比例较低；（2）C末端稳定性降低；（3）缺少一个温适应胰蛋白酶保守的脯氨酸残基和一个脯氨酸 - 酪氨酸堆积；（4）延伸结合口袋的环的电荷和柔韧性存在差异；（5）“自溶”环的构象不同，该环可能参与底物结合。
