α水晶體蛋白是小熱休克性家族的一員。為了研究其結構與類似伴護活性之關係，我們利用定點突變將αA水晶體蛋白的Asp69位置突變成帶正電的Arg殘基和疏水性的Trp殘基。和重組的αA水晶體蛋白比較，突變的D69R和D69W顯示相似的二級與三級結構。ANS螢光顯示這兩個突變的蛋白質有較高的疏水性。突變D69R和重組的αA水晶體蛋白有相似的伴護活性，但是D69W已幾乎喪失其伴護活性。突變的D69R與D69W的熱穩定性低於天然的α水晶體蛋白與重組的αA水晶體蛋白。隨著預熱溫度的升高，重組的αA水晶體蛋白和D69R的伴護活性隨之增加，但是D69W仍然沒有伴護活性。因此，在αA水晶體蛋白中，此位置必須存在親水性殘基，以維持其結構與功能的完整性。

　α-Crystallin is a members of the family of small-heat-shock proteins.To investigate the structure and chaperone-like activity relationship, wereplaced Asp69 in rat lens αA-crystallin with a positive charged Argresidue and with a hydrophobic Trp residue respectively by site-directedmutagenesis. In comparison with the recombinant αA-crystallin, themutant proteins D69R and D69W displayed similar secondary structureand tertiary structure. ANS fluorescence showed a little higherhydrophobicity for both mutant proteins. Mutant D69R showed similarchaperone-like activity as the recombinant αA-crystallin, whereas mutantD69W showed dramatic changes in the chaperone-like activity. Thermalstability of both D69R and D69W were lower than that of native andrecombinant αA-crystallin. The chaperone-like activity of recombinantαA-crystallin and D69R were enhanced with the increase of temperature,but D69W still showed little chaperone-like activity. Thus, a hydrophilicresidue must be preserved at this position to maintain its structural andfunctional integrity of αA-crystallin.

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