Conformational properties of substrate proteins bound to a molecular chaperone alpha-crystallin
Conformational properties of substrate proteins bound to a molecular chaperone alpha-crystallin
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DOI：
10.1074/jbc.271.18.10449
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发表时间：
1996-05-03
影响因子：
4.8
通讯作者：
Surewicz, WK
中科院分区：
文献类型：
--
作者：
Das, KP;Petrash, JM;Surewicz, WK
晶状体的主要蛋白- α -晶体蛋白作为分子伴侣，抑制受损蛋白的非特异性聚集。为了研究α - a-晶体蛋白与底物蛋白相互作用的机制，我们制备了一种不含色氨酸的人α - a-晶体蛋白突变体，并利用荧光光谱分析了该突变体捕获的热不稳定蛋白的构象。结合底物（罗丹斯和γ -晶体蛋白）的荧光发射特性和荧光猝灭实验结果表明，α -晶体蛋白捕获的蛋白质具有非常低的展开程度。特别是，与α - a -晶体蛋白结合的罗丹斯酶的结构似乎比与伴侣蛋白GroEL结合的酶的结构更像天然的。我们假设α -结晶蛋白（可能还有其他小的热休克蛋白）优先识别在变性途径中很早就发生的易于聚集的构象。凭借其捕获和稳定这些早期非天然结构的能力，α -晶体蛋白似乎是唯一适合陪伴晶状体透明特性的蛋白。
alpha-Crystallin, the major protein of the ocular lens, acts as a molecular chaperone by suppressing the nonspecific aggregation of damaged proteins. To investigate the mechanism of the interaction between alpha-crystallin and substrate proteins, we prepared a tryptophan-free mutant of human alpha A-crystallin and assessed the conformation of thermally destabilized proteins captured by this chaperone using fluorescence spectroscopy. The fluorescence emission characteristics of bound substrates (rhodanese and gamma-crystallin) and the results of fluorescence quenching experiments indicate that the proteins captured by alpha-crystallin are characterized by a very low degree of unfolding. In particular, the structure of rhodanese bound to alpha A-crystallin appears to be considerably more native-like compared to that of the enzyme bound to the chaperonin GroEL. We postulate that alpha-crystallin (and likely other small heat shock proteins) recognize preferentially the aggregation-prone conformers that occur very early on the denaturation pathway. With its ability to capture and stabilize these early non-native structures, alpha-crystallin appears to be uniquely well suited to chaperone the transparency properties of the ocular lens.