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首页> 外文期刊>Journal of Molecular Biology >Heat-induced unfolding of neocarzinostatin, a small all-beta protein investigated by small-angle X-ray scattering.
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Heat-induced unfolding of neocarzinostatin, a small all-beta protein investigated by small-angle X-ray scattering.

机译：热诱导的新carcarinostatin的展开，新的carzinostatin是一种通过小角度X射线散射研究的小全β蛋白。

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Neocarzinostatin is an all-beta protein, 113 amino acid residues long, with an immunoglobulin-like fold. Its thermal unfolding has been studied by small-angle X-ray scattering. Preliminary differential scanning calorimetry and fluorescence measurements suggest that the transition is not a simple, two-state transition. The apparent radius of gyration is determined using three different approaches, the validity of which is critically assessed using our experimental data as well as a simple, two-state model. Similarly, each step of data analysis is evaluated and the underlying assumptions plainly stated. The existence of at least one intermediate state is formally demonstrated by a singular value decomposition of the set of scattering patterns. We assume that the pattern of the solution before the onset of the transition is that of the native protein, and that of the solution at the highest temperature is that of the completely unfolded protein. Given these, actually not very restrictive, boundary constraints, a least-squares procedure yields a scattering pattern of the intermediate state. However, this solution is not unique: a whole class of possible solutions is derived by adding to the previous linear combination of the native and completely unfolded states. Varying the initial conditions of the least-squares calculation leads to very similar solutions. Whatever member of the class is considered, the conformation of this intermediate state appears to be weakly structured, probably less than the transition state should be according to some proposals. Finally, we tried and used the classical model of three thermodynamically well-defined states to account for our data. The failure of the simple thermodynamic model suggests that there is more than the single intermediate structure required by singular value decomposition analysis. Formally, there could be several discrete intermediate species at equilibrium, or an ensemble of conformations differently populated according to the temperature. In the latter case, a third state would be a weighted average of all non native and not completely unfolded states of the protein but, since the weights change with temperature, no meaningful curve is likely to be derived by a global analysis using the simple model of three thermodynamically well-defined states. Copyright 2001 Academic Press.
机译：新卡他汀是一种全β蛋白，长113个氨基酸残基，具有类似免疫球蛋白的折叠。通过小角度X射线散射研究了其热展开。初步的差示扫描量热法和荧光测量表明，该转变不是简单的两态转变。旋转的视半径是通过三种不同的方法确定的，其有效性通过我们的实验数据以及简单的两态模型进行了严格评估。同样，对数据分析的每个步骤都进行了评估，并明确陈述了基本假设。至少一个中间状态的存在通过一组散射图案的奇异值分解来正式证明。我们假设在过渡开始之前溶液的模式是天然蛋白质的模式，而在最高温度下溶液的模式是完全展开的蛋白质的模式。给定这些实际上不是很严格的边界约束，最小二乘法会产生中间状态的散射图。但是，这种解决方案不是唯一的：通过将原始状态和完全展开状态的线性组合添加到以前的组合中，可以得出一整类可能的解决方案。改变最小二乘计算的初始条件会导致非常相似的解决方案。无论考虑到该类的任何成员，该中间状态的构象似乎都是结构较弱的，可能比某些建议所建议的过渡状态要少。最后，我们尝试并使用了三个热力学定义明确的状态的经典模型来解释我们的数据。简单热力学模型的失败表明，奇异值分解分析需要的不仅仅是单个中间结构。从形式上讲，可能有几个离散的中间物种处于平衡状态，或者根据温度不同而组成的一组构象。在后一种情况下，第三种状态将是蛋白质的所有非天然状态和未完全展开状态的加权平均值，但是，由于权重随温度变化，因此使用简单模型进行的全局分析可能不会得出有意义的曲线三个热力学定义明确的状态。版权所有2001学术出版社。

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