Selective degradation of oxidized calmodulin by the 20 S proteasome
Selective degradation of oxidized calmodulin by the 20 S proteasome
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DOI：
10.1074/jbc.m005356200
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发表时间：
2001-01-12
影响因子：
4.8
通讯作者：
Squier, TC
中科院分区：
文献类型：
--
作者：
Ferrington, DA;Sun, HY;Squier, TC
我们已经研究了靶向氧化钙调素被蛋白酶体降解的机制。在钙调素内的甲硫氨酸氧化后，20 S蛋白酶体的降解速率显著增强。质谱法用于鉴定从蛋白酶体释放的蛋白水解片段的时间过程。氧化的钙调蛋白最初降解成从蛋白酶体释放的大的蛋白水解片段，随后降解成大小从6至12个氨基酸不等的小肽。为了研究导致氧化钙调素选择性降解的分子决定因素，我们使用圆二色谱和荧光光谱来评估氧化剂诱导的结构变化。二级结构的降低与降解速率之间存在线性相关性。钙结合或通过甲硫氨酸亚砜还原酶修复氧化钙调蛋白诱导α-螺旋含量和降解速率的可比变化。相反，氧化钙调蛋白的表面疏水性的改变不改变蛋白酶体的降解速率，表明表面疏水性的变化不一定导致蛋白水解敏感性的增强。这些结果表明，在二级结构的减少暴露在氧化钙调蛋白的蛋白水解敏感位点被切割的蛋白酶体在一个nonprocessive的方式。
We have investigated the mechanisms that target oxidized calmodulin for degradation by the proteasome, After methionine oxidation within calmodulin, rates of degradation by the 20 S proteasome are substantially enhanced. Mass spectrometry was used to identify the time course of the proteolytic fragments released from the proteasome. Oxidized calmodulin is initially degraded into large proteolytic fragments that are released from the proteasome and subsequently degraded into small peptides that vary in size from 6 to 12 amino acids. To investigate the molecular determinants that result in the selective degradation of oxidized calmodulin, we used circular dichroism and fluorescence spectroscopy to assess oxidant-induced structural changes. There is a linear correlation between decreases in secondary structure and the rate of degradation. Calcium binding or the repair of oxidized calmodulin by methionine sulfoxide reductase induces comparable changes in alpha -helical content and rates of degradation. In contrast, alterations in the surface hydrophobicity of oxidized calmodulin do not alter the rate of degradation by the proteasome, indicating that changes in surface hydrophobicity do not necessarily lead to enhanced proteolytic susceptibility. These results suggest that decreases in secondary structure expose proteolytically sensitive sites in oxidized calmodulin that are cleaved by the proteasome in a nonprocessive manner.