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首页> 外文期刊>Journal of Molecular Biology >VIBRATIONAL RAMAN OPTICAL ACTIVITY OF ALPHA-LACTALBUMIN - COMPARISON WITH LYSOZYME, AND EVIDENCE FOR NATIVE TERTIARY FOLDS IN MOLTEN GLOBULE STATES
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VIBRATIONAL RAMAN OPTICAL ACTIVITY OF ALPHA-LACTALBUMIN - COMPARISON WITH LYSOZYME, AND EVIDENCE FOR NATIVE TERTIARY FOLDS IN MOLTEN GLOBULE STATES

机译：α-乳白蛋白的振动拉曼光学活性与溶菌酶的比较，以及在球形状态下原始三元折叠的证据

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Proteins in aqueous solution are now accessible to Raman optical activity (ROA) measurements, which provide an incisive new probe of secondary and tertiary structure illustrated here by a study of bovine alpha-lactalbumin. The room-temperature ROA spectrum of native bovine alpha-lactalbumin is similar to that of native hen egg-white lysozyme except for features attributable to differences in the loop regions: in particular, a positive ROA band at similar to 1338 cm(-1) assigned to conformationally homogeneous loop structure, possibly with local order corresponding to 3(10)-helix, has more than double the intensity in alpha-lactalbumin compared with lysozyme. This is consistent with the two proteins having similar secondary structure but different local details in the tertiary fold. ROA measurements on alpha-lactalbumin at pH 2.0 over a range of temperatures have provided a new perspective on the molten globule state. Thus at 35 degrees C ROA reveals the presence of some secondary structure but an almost complete loss of the tertiary loop structure; whereas at 2 degrees C the ROA spectrum is almost identical with that of the native protein, which is strong evidence that virtually all of the secondary structure and the tertiary backbone fold persist, albeit within a looser framework associated with increased solvent exposure and change of environment of many of the side-chains as evidenced by an increase in noise and bandwidth of some of the ROA signals together with aromatic fluorescence and near-UV circular dichroism signals characteristic of the molten globule state. Our sample of acid alpha-lactalbumin at 2 degrees C therefore appears to be an archetypal example of Ptitsyn's ''native-like'' molten globule, having a fixed native-like tertiary fold but with loss of tight packing of the side-chains; whereas at 35 degrees C it is a ''disordered'' molten globule. At 20 degrees C the acid molten globule appears to retain highly native-like secondary structure but with most of the tertiary fold already lost. A calcium-free sample of alpha-lactalbumin at neutral pH displayed a broad cooperative transition between native and molten globule states at similar to 15 degrees C, with the latter state showing similar but somewhat degraded tertiary loop ROA signatures to the native protein. In both the acid and apo molten globule states the ROA signatures of the secondary structure and the tertiary loops showed a gradual change with temperature. (C) 1995 Academic Press Limited [References: 70]
机译：现在可以通过拉曼光学活性（ROA）测量来获取水溶液中的蛋白质，通过对牛α-乳白蛋白的研究，该蛋白提供了一种敏锐的二级和三级结构新探针。天然牛α-乳白蛋白的室温ROA谱与天然母鸡蛋清溶菌酶的室温谱相似，除了归因于环区域差异的特征外：特别是在类似于1338 cm（-1）的正ROA带上与溶菌酶相比，被赋予构象均一的环状结构（可能具有对应于3（10）-螺旋的局部顺序）的α-乳清蛋白的强度是其两倍以上。这与具有相似二级结构但在三级折叠中具有不同局部细节的两种蛋白质是一致的。在一定温度范围内，在pH 2.0的α-乳白蛋白上的ROA测量结果为熔融小球的状态提供了新的视角。因此，在35摄氏度时，ROA揭示了一些二级结构的存在，但是三级环结构几乎完全丧失了;而在2摄氏度时，ROA谱图几乎与天然蛋白的谱图相同，这有力证据表明，尽管在与溶剂接触量增加和环境变化相关的较宽松框架内，几乎所有二级结构和三级主链折叠仍然存在某些ROA信号的噪声和带宽的增加，以及熔融球状状态所特有的芳香族荧光和近紫外圆二色性信号的增加，证明了许多侧链的分布。因此，我们在2摄氏度的酸性α-乳清蛋白样品似乎是Ptitsyn的“天然样”熔融小球的原型实例，具有固定的天然样三级折叠，但侧链紧密堆积。而在35摄氏度时，它是“无序的”熔融小球。在20摄氏度时，酸性熔融小球似乎保留了高度天然的二级结构，但大部分三级折叠已丢失。在中性pH值下，无钙的α-乳清蛋白样品在接近15摄氏度的天然和熔融小球状态之间显示出广泛的协同过渡，后者状态显示出与天然蛋白质相似但略微降解的叔环ROA签名。在酸性和载脂蛋白熔融小球状态下，二级结构的ROA标记都呈现出来，三级环显示出随温度的逐渐变化。 （C）1995 Academic Press Limited [参考号：70]

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