Nakamura Tooru, Sadakane Yutaka, Fujii Noriko
Research Reactor Institute, Kyoto University, Kumatori, Sennan, Osaka 590-0494, Japan.
Biochim Biophys Acta. 2006 Apr;1764(4):800-6. doi: 10.1016/j.bbapap.2006.02.005. Epub 2006 Mar 13.
Asp58 and Asp151 in human lens alphaA-crystallin invert and isomerize to d-beta-aspartyl residues with age. Here, we report that the racemization rate constants (k) of Asp58 and Asp151 residues in human recombinant alphaA-crystallin at 37 degrees C are 3.72 +/- 0.8 x 10(-4) and 10.7 +/- 0.7 x 10(-4)/day, respectively. The activation energy of racemization of Asp58 and Asp151 in the protein was 27.0 +/- 0.5 kcal/mol and 21.0 +/- 0.5 kcal/mol, respectively. The time required for the D/L ratio of Asp58 and Asp151 to approximate to 1.0 (D/L ratio of Asp = 0.99) at 37 degrees C was estimated as 20.9 +/- 3.7 and 6.80 +/- 0.4 years, respectively. Thus, Asp151 is more susceptible to racemization than Asp58, consistent with data from short model peptides. However, the racemization rates of both Asp58 and Asp151 residues in the protein were twice as rapid as in model peptides. These results indicate that the racemization of Asp residues in alphaA-crystallin may be influenced not only by the primary structure but also by the higher order structure around Asp residues in the protein.
随着年龄增长，人晶状体αA-晶状体蛋白中的天冬氨酸58（Asp58）和天冬氨酸151（Asp151）会发生构型反转并异构化为d-β-天冬氨酰残基。在此，我们报告，人重组αA-晶状体蛋白中Asp58和Asp151残基在37℃时的消旋速率常数（k）分别为3.72±0.8×10⁻⁴和10.7±0.7×10⁻⁴/天。该蛋白中Asp58和Asp151消旋的活化能分别为27.0±0.5千卡/摩尔和21.0±0.5千卡/摩尔。在37℃时，Asp58和Asp151的D/L比值接近1.0（Asp的D/L比值 = 0.99）所需的时间分别估计为20.9±3.7年和6.80±0.4年。因此，Asp151比Asp58更容易发生消旋，这与短模型肽的数据一致。然而，该蛋白中Asp58和Asp151残基的消旋速率是模型肽中的两倍。这些结果表明，αA-晶状体蛋白中天冬氨酸残基的消旋可能不仅受一级结构影响，还受该蛋白中天冬氨酸残基周围高级结构的影响。
