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首页> 外文期刊>Journal of Molecular Biology >A new folding intermediate of apomyoglobin from Aplysia limacina: stepwise formation of a molten globule.
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A new folding intermediate of apomyoglobin from Aplysia limacina: stepwise formation of a molten globule.

机译：来自Aplysia limacina的磷肌红蛋白的新折叠中间体：逐步形成熔融小球。

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摘要

Apomyoglobin from Aplysia limacina (al-apoMb), despite having only 20 % sequence identity with the more commonly studied mammalian globins (m-apoMbs), properties which result in an increased number of hydrophobic contacts and a loss of most internal salt bridges, shares a number of features of their folding profiles. We show here that it contains an unusually stable core which resists unfolding even at 70 degrees C. The equilibrium intermediate (I(T)) at this high temperature is distinct from the acid unfolded state I(A) which has many properties in common with the acid intermediate observed for the mammalian apoproteins (I(AGH)). It contains a smaller amount of secondary structure (27 % alpha-helical instead of 35 %) and is more highly solvated as evidenced from its fluorescence spectrum (lambda(max)=344 nm instead of 338 nm). Its stability is greatly increased (DeltaDeltaG(w)=-6.75 kcal mol(-1)) in the presence of high salt (2 M KCl), lending support to the view that hydrophobic interactions are responsible for its stability. Kinetic data show classical two-state kinetics between I(A) and the folded state both in the presence and absence of salt. Both I(A) and I(T) can be populated within the dead time of the stopped-flow apparatus, since initiating the refolding reaction from I(T) or I(A) rather than the completely unfolded state does not affect the observed refolding time-course. Our conclusion is that al-apoMb, as other "apo" proteins (including for example alpha-lactalbumin in the absence of Ca(2+)), may be described as "uncoupled" with an unusually high and exploitable tendency to populate partially folded states. Copyright 2000 Academic Press.
机译：尽管与更普遍研究的哺乳动物球蛋白（m-apoMbs）仅具有20％的序列同一性，但来自Aplysia limacina的Apomyoglobin（al-apoMb）的特性导致疏水性接触数量增加和大部分内部盐桥的损失，折叠型材的许多功能。我们在这里表明，它包含一个异常稳定的核，即使在70摄氏度时，它也能抵抗解折叠。在这种高温下，平衡中间体（I（T））与酸解折叠状态I（A）截然不同，后者具有许多共同的特性观察到的哺乳动物载脂蛋白（I（AGH））的酸性中间体。它包含较少量的二级结构（27％的α-螺旋而不是35％），并且从其荧光光谱（λ（max）= 344 nm而不是338 nm）中可以看出，溶剂化程度更高。在高盐（2 M KCl）存在的情况下，其稳定性大大提高（DeltaDeltaG（w）=-6.75 kcal mol（-1）），从而支持了疏水相互作用为其稳定性负责的观点。动力学数据表明在有盐和无盐情况下，I（A）和折叠态之间的经典二态动力学。 I（A）和I（T）都可以在停流设备的停滞时间内填充，因为从I（T）或I（A）引发重折叠反应而不是完全展开状态不会影响观察到的结果重复时间过程。我们的结论是，作为其他“ apo”蛋白（包括例如在缺少Ca（2+）的情况下的α-乳清蛋白）的al-apoMb，可被描述为“解偶联”，具有异常高且可利用的部分折叠趋势状态。版权所有2000学术出版社。

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