Biswas Ashis, Das Kali P
Protein Chemistry Laboratory, Department of Chemistry, Bose Institute, 93/1 APC Road, Kolkata 700 009, India.
Biochemistry. 2008 Jan 15;47(2):804-16. doi: 10.1021/bi7011965. Epub 2007 Dec 21.
Alpha-crystallin, the major eye lens protein, is a molecular chaperone that plays a crucial role in the suppression of protein aggregation and thus in the long-term maintenance of lens transparency. Zinc is a micronutrient of the eye, but its molecular interaction with alpha-crystallin has not been studied in detail. In this paper, we present results of in vitro experiments that show bivalent zinc specifically interacts with alpha-crystallin with a dissociation constant in the submillimolar range (Kd approximately 0.2-0.4 mM). We compared the effect of Zn2+ with those of Ca2+, Cu2+, Mg2+, Cd2+, Pb2+, Ni2+, Fe2+, and Co2+ at 1 mM on the structure and chaperoning ability of alpha-crystallin. An insulin aggregation assay showed that among the bivalent metal ions, only 1 mM Zn2+ improved the chaperone function of alpha-crystallin by 30% compared to that in the absence of bivalent metal ions. Addition of 1 mM Zn2+ increased the yield of alpha-crystallin-assisted refolding of urea-treated LDH to its native state from 33 to 38%, but other bivalent ions had little effect. The surface hydrophobicity of alpha-crystallin was increased by 50% due to the binding of Zn2+. In the presence of 1 mM Zn2+, the stability of alpha-crystallin was enhanced by 36 kJ/mol, and it became more resistant to tryptic cleavage. The implications of enhanced stability and molecular chaperone activity of alpha-crystallin in the presence of Zn2+ are discussed in terms of its role in the long-term maintenance of lens transparency and cataract formation.
α-晶状体蛋白是眼晶状体的主要蛋白质，是一种分子伴侣，在抑制蛋白质聚集以及维持晶状体长期透明性方面发挥着关键作用。锌是眼睛的一种微量营养素，但其与α-晶状体蛋白的分子相互作用尚未得到详细研究。在本文中，我们展示了体外实验结果，结果表明二价锌与α-晶状体蛋白特异性相互作用，解离常数在亚毫摩尔范围内（Kd约为0.2 - 0.4 mM）。我们比较了1 mM的Zn2+与Ca2+、Cu2+、Mg2+、Cd2+、Pb2+、Ni2+、Fe2+和Co2+对α-晶状体蛋白结构和伴侣功能的影响。胰岛素聚集试验表明，在二价金属离子中，与不存在二价金属离子相比，只有1 mM Zn2+能使α-晶状体蛋白的伴侣功能提高30%。添加1 mM Zn2+可使α-晶状体蛋白辅助尿素处理的乳酸脱氢酶重折叠至天然状态的产率从33%提高到38%，但其他二价离子几乎没有影响。由于Zn2+的结合，α-晶状体蛋白的表面疏水性增加了50%。在1 mM Zn2+存在下，α-晶状体蛋白的稳定性提高了36 kJ/mol，并且对胰蛋白酶切割更具抗性。本文从α-晶状体蛋白在维持晶状体长期透明性和白内障形成中的作用方面，讨论了在Zn2+存在下其稳定性增强和分子伴侣活性增强的意义。
