National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India; Indian Institute of Science Education and Research, Pune, India. Electronic address: https://twitter.com/Rupam_B01.
National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India; Indian Institute of Science Education and Research, Pune, India.
J Mol Biol. 2021 Nov 19;433(23):167268. doi: 10.1016/j.jmb.2021.167268. Epub 2021 Sep 23.
Little is known about how the sequence of structural changes in one chain of a heterodimeric protein is coupled to those in the other chain during protein folding and unfolding reactions, and whether individual secondary structural changes in the two chains occur in one or many coordinated steps. Here, the unfolding mechanism of a small heterodimeric protein, double chain monellin, has been characterized using hydrogen exchange-mass spectrometry. Transient structure opening, which enables HX, was found to be describable by a five state N ↔ I ↔ I ↔ I ↔ U mechanism. Structural changes occur gradually in the first three steps, and cooperatively in the last step. β strands 2, 4 and 5, as well as the α-helix undergo transient unfolding during all three non-cooperative steps, while β1 and the two loops on both sides of the helix undergo transient unfolding during the first two steps. In the absence of GdnHCl, only β3 in chain A of the protein unfolds during the last cooperative step, while in the presence of 1 M GdnHCl, not only β3, but also β2 in chain B unfolds cooperatively. Hence, the extent of cooperative structural change and size of the cooperative unfolding unit increase when the protein is destabilized by denaturant. The naturally evolved two-chain variant of monellin folds and unfolds in a more cooperative manner than does a single chain variant created artificially, suggesting that increasing folding cooperativity, even at the cost of decreasing stability, may be a driving force in the evolution of proteins.
关于在蛋白质折叠和展开反应中，杂二聚体蛋白的一条链的结构变化序列如何与另一条链的结构变化序列偶联，以及两条链中的各个二级结构变化是否发生在一个或多个协调的步骤中，人们知之甚少。在这里，使用氢交换 - 质谱法对一种小的杂二聚体蛋白双链莫内林的展开机制进行了表征。发现瞬态结构打开（可进行 HX）可通过五态 N↔I↔I↔I↔U 机制来描述。前三个步骤中的结构变化逐渐发生，最后一个步骤中协同发生。β 链 2、4 和 5 以及 α-螺旋在所有三个非协同步骤中都会发生短暂的展开，而 β1 和螺旋两侧的两个环在前两个步骤中会发生短暂的展开。在没有 GdnHCl 的情况下，只有蛋白质 A 链中的β3 在最后一个协同步骤中展开，而在存在 1 M GdnHCl 的情况下，不仅β3，而且 B 链中的β2 也协同展开。因此，当蛋白质被变性剂失稳时，协同结构变化的程度和协同展开单元的大小增加。与人工创建的单链变体相比，天然进化的双链变体以更协同的方式折叠和展开，这表明增加折叠协同性，即使以降低稳定性为代价，也可能是蛋白质进化的驱动力。
