HUMAN AND RODENT ALZHEIMER BETA-AMYLOID PEPTIDES ACQUIRE DISTINCT CONFORMATIONS IN MEMBRANE-MIMICKING SOLVENTS
HUMAN AND RODENT ALZHEIMER BETA-AMYLOID PEPTIDES ACQUIRE DISTINCT CONFORMATIONS IN MEMBRANE-MIMICKING SOLVENTS
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DOI：
10.1111/j.1432-1033.1993.tb19893.x
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发表时间：
1993-01-15
期刊：
影响因子：
--
通讯作者：
MANTSCH, HH
中科院分区：
文献类型：
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作者：
OTVOS, L;SZENDREI, GI;MANTSCH, HH
老年斑（阿尔茨海默病的标志性病变之一）的主要成分是42（43）-氨基酸多肽，称为A4或β-淀粉样肽。β-淀粉样肽或A4衍生自一种或多种较大的β-淀粉样前体蛋白。A4肽的前体蛋白在整个进化过程中是高度保守的，人类、猴子、狗和熊在淀粉样纤维中形成了A4肽的大脑沉积物。然而，在大鼠和小鼠的大脑中，A4淀粉样蛋白的类似积累是可以忽略不计的，原因尚未探索。值得注意的是，从cDNA克隆中推导出的啮齿动物的A4序列与从人脑中分离的A4仅在三个氨基酸上不同。因此，这些差异可以解释啮齿类动物不能发展阿尔茨海默病样A4淀粉样斑块。为了直接测试这一假设，使用物理和化学模型系统，我们合成、纯化和表征了对应于人类和啮齿动物序列的A4肽。圆二色性和傅里叶变换红外光谱与各种膜模拟溶剂，不同的肽浓度，和可变的pH值，以确定那些环境条件，促进β-折叠片形成的人与啮齿动物A4。在中等碱性pH（小于或等于10）下，啮齿动物肽具有比人序列更多的折叠片结构。两种肽的β-折叠片层可以在非常高的pH（大于或等于12）下消除。与SDS中以及此处测试的几种其他溶液中发现的β-结构相比，辛基葡糖苷溶液中的β-结构的量增加。这表明源自先前膜损伤的颗粒可能在β-折叠片层的稳定中起作用，随后形成淀粉样蛋白沉积物。最后，我们发现在乙腈/水混合物中的啮齿动物序列中观察到更高的β-折叠片含量。相比之下，更多的β-折叠片检测与人类A4在三氟乙醇/水的混合物在中性pH值。值得注意的是，在相对较低的肽浓度，只有人类序列假定一个扩展的二级结构。这些数据表明，细微的种间氨基酸差异可能是啮齿动物肽不能在原位形成淀粉样纤维的原因。
The major constituent of senile plaques (one of the hallmark lesions of Alzheimer's disease) is a 42(43)-amino-acid polypeptide, termed the A4 or beta-amyloid peptide. The beta-amyloid peptide or A4 is derived from one or more larger beta-amyloid precursor proteins. The precursor protein from whence the A4 peptide is derived is highly conserved throughout evolution, and humans, monkeys, dogs, and bears develop brain deposits of A4 peptide in amyloid fibrils. However, similar accumulations of A4 amyloid are negligible in the brains of rats and mice for reasons that remain unexplored. Notably, the A4 sequence of rodents, deduced from the cDNA clones, differs only in three amino acids from the A4 isolated from the brain of humans. Hence, these differences could account for the inability of rodents to develop Alzheimer-like A4 amyloid plaques. To test this hypothesis directly, using physical and chemical model systems, we synthesized, purified, and characterized A4 peptides corresponding to the human and rodent sequences. Circular dichroic and Fourier-transform infrared spectroscopy were used with various membrane-mimicking solvents, different peptide concentrations, and variable pH to identify those environmental conditions that promoted beta-pleated sheet formation of the human versus rodent A4. At an intermediate alkaline pH (less-than-or-equal-to 10), the rodent peptide has more beta-pleated sheet structure than the human sequence. The beta-pleated sheets for both peptides could be eliminated at very high pH (greater-than-or-equal-to 12). The amount of the beta-structure increased in an octyl glucoside solution, compared to that found in SDS, as well as in several of the other solutions tested here. This suggests that particles originated from prior membrane damage may play a role in the stabilization of beta-pleated sheets with subsequent formation of amyloid deposits. Finally, we found that higher beta-pleated sheet content was observed for the rodent sequences in acetonitrile/water mixtures. In contrast, more beta-pleated sheets were detected with the human A4 in trifluoroethanol/water mixtures at neutral pH. Remarkably, at relatively low peptide concentrations, only the human sequence assumed an extended secondary structure. These data suggest that subtle inter-species amino-acid differences may account for the inability of the rodent peptide to form amyloid fibrils in situ.