Enzyme surface rigidity tunes the temperature dependence of catalytic rates
Enzyme surface rigidity tunes the temperature dependence of catalytic rates
复制标题
DOI：
10.1073/pnas.1605237113
复制
发表时间：
2016-07-12
影响因子：
11.1
通讯作者：
Brandsdal, Bjorn Olav
中科院分区：
文献类型：
--
作者：
Isaksen, Geir Villy;Aqvist, Johan;Brandsdal, Bjorn Olav
酶适应低温的结构起源，即使在水的冰点附近也能有效地催化化学反应，这仍然是生物催化中的一个基本难题。所有冷活性酶都有一个显著的共同特征，那就是活化能降低，同时伴随着更负的熵，这缓解了温度降低导致的化学反应速度的指数下降。在这里，我们探索蛋白质表面迁移率在决定这一焓-熵平衡中的作用。本文利用大量的计算机模拟，通过高精度的Arrhenius曲线图和多肽水解反应的热力学活化参数的计算，证明了修饰冷活性和温活性胰酶的表面刚性的效果。通过施加位置限制，系统地改变蛋白质表面的柔韧性，在不改变氨基酸序列的情况下，使冷活性胰酶变成具有中温特性的变体的显著效果。此外，我们还表明，仅仅抑制一个关键表面环路就会产生与该环路中冷活性和温活性胰酶之间的点突变相同的效果。重要的是，在室温下，高达10千卡/摩尔的活化热-熵平衡的变化几乎是完全平衡的，而对于冷适应酶来说，它们在低温下产生的速率要高得多。
The structural origin of enzyme adaptation to low temperature, allowing efficient catalysis of chemical reactions even near the freezing point of water, remains a fundamental puzzle in biocatalysis. A remarkable universal fingerprint shared by all cold-active enzymes is a reduction of the activation enthalpy accompanied by a more negative entropy, which alleviates the exponential decrease in chemical reaction rates caused by lowering of the temperature. Herein, we explore the role of protein surface mobility in determining this enthalpy-entropy balance. The effects of modifying surface rigidity in cold-and warm-active trypsins are demonstrated here by calculation of high-precision Arrhenius plots and thermodynamic activation parameters for the peptide hydrolysis reaction, using extensive computer simulations. The protein surface flexibility is systematically varied by applying positional restraints, causing the remarkable effect of turning the cold-active trypsin into a variant with mesophilic characteristics without changing the amino acid sequence. Furthermore, we show that just restraining a key surface loop causes the same effect as a point mutation in that loop between the cold-and warm-active trypsin. Importantly, changes in the activation enthalpy-entropy balance of up to 10 kcal/mol are almost perfectly balanced at room temperature, whereas they yield significantly higher rates at low temperatures for the cold-adapted enzyme.