 α 水晶體蛋白是脊椎動物水晶體中主要的蛋白質，包含αA和αB兩種單體，而在囓齒動物中另含有αAins單體。α水晶體蛋白和small heat shock proteins是屬於同源性蛋白質，且具有分子伴護功能。為了進行結構和功能上的研究，我們利用基因重組的方式得到在N端含有組胺酸標籤(Histidine-tag)的αA水晶體蛋白及突變株F71W、F71R。在類伴護活性分析中αA水晶體蛋白與突變株F71W有較相似的伴護活性，然而F71R具有較差的伴護活性。遠紫外光區圓二色光譜分析的結果可以得知αA水晶體蛋白和突變株F71W的二級結構較為相似，而F71R在β-turn的比例相較於αA水晶體蛋白和突變株F71W分別降低50 %和30 %。而在近紫外光區圓二色光譜分析中顯示αA水晶體蛋白與突變株F71W和F71R在三級結構上有明顯的差異。ANS螢光光譜分析顯示αA水晶體蛋白突變株F71W 、F71R所暴露出的疏水性表面較αA水晶體蛋白多。從一系列的熱穩定分析中，可以發現αA水晶體蛋白在室溫時有較少的高子量集結體且熱穩定性最佳。在室溫至55℃之間，αA水晶體蛋白與突變株F71W、F71R，隨著溫度增加，暴露出來的表面疏水性有增加的趨勢，但只有αA水晶體蛋白之伴護活性隨著溫度增加而增加。我們的實驗結果顯示(1)組胺酸標籤對於結構和伴護活性有些許的影響、(2)αA水晶體蛋白中Phe71的疏水性殘基的存在對結構和伴護活性有其重要性、(3)當αA水晶體蛋白中Phe71的疏水性殘基置換成親水性且帶電荷的殘基時，更易聚集成高分子集結體且有較多的表面疏水性暴露出、(4)暴露出來的表面疏水性越多並不代表伴護活性越高。

 α Crystallin, the major component of lens proteins, includes αA and αB two subunits in vertebrate eye lenses and a third additional αAins subunit in rodents eye lenses. α-Crystallin is known to have chaperone-like behavior and is shown to have homology with small heat shock proteins in amino acid sequence. In order to study the structure-functionality relationship, we have reconstituted wild type αA (αA-wt) and mutant αA-F71W and αA-F71R all with extra histidine tag in N-terminal. It is found that αA-F71W showed comparative activity with αA-wt, while as F71R showed much less activity. Secondary components of the these three reconstituted proteins based on far UV-CD spectroscopy showed αA-F71W and αA-wt have similar percentage of secondary components; while αA-F71R showed different constitution with having about 50% and 30% lower in β-turn percentage compared respectively with αA-wt and αA-F71W. Near UV-CD spectra show quite different compared αA-wt with the two mutation αA-crystallins. ANS fluorescence study showed αA-F71W and αA-F71R were more hydrophobic than αA-wt. Thermal stability analyses showed that αA-wt was less aggregative in room temperature and more stable in higher temperature. αA-F71R showed more potent to aggregate into high molecular aggregates (greater than 2000 kDa) at room temperature. The surface hydrophobicity increased with the increase of temperature between 25 ℃ and 55 ℃; however, for chaperone activity only αA-wt showed the same potent. Our studies showed that i) the extra histidine tag has little effects on the crystalline structure and chaperone activity; ii) right size hydrophobic residue at amino acid 71 is important in maintaining its structure and activity; iii) Replacing amino acid 71with charged hydrophilic residue results in more potent of aggregating into high molecular aggregates and higher surface hydrophobicity. iv) More hydrophobic surface exposed does not mean more chaperone activity.

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