Enhanced C-terminal truncation of alphaA- and alphaB-crystallins in diabetic lenses.
Enhanced C-terminal truncation of alphaA- and alphaB-crystallins in diabetic lenses.
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发表时间：
2002-10
影响因子：
4.4
通讯作者：
P. Thampi;Azeem Hassan;Jean B. Smith;E. Abraham
中科院分区：
文献类型：
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作者：
P. Thampi;Azeem Hassan;Jean B. Smith;E. Abraham
目的研究糖尿病对人和大鼠晶状体α A和α B晶体蛋白C-末端氨基酸残基裂解的影响。方法：人类晶状体是来自57岁、59岁、69岁和72岁供体的糖尿病或年龄匹配的对照晶状体。还从链脲佐菌素诱导的糖尿病大鼠中获得晶状体。通过凝胶渗透色谱法分离水溶性级分中的单个透镜晶体蛋白。通过电喷雾电离质谱法分析高（alphaH）和低（alphaL）分子量馏分。结果：人晶状体α A-晶状体蛋白的典型质谱图显示了完整的未修饰的α A-晶状体蛋白、截短的α A（1-172）和单磷酸化的α A-晶状体蛋白。糖尿病镜片显示出比对照镜片高近两倍的alphaA（1-172）水平。此外，alphaH级分始终显示出比alphaL级分显著更高的alphaA（1-172）水平。人α B-晶状体蛋白未显示C-末端截短的证据。大鼠α A-晶状体蛋白有五个C-末端截短的成分，其中大部分在糖尿病中表现出大幅增加。截短的α A（1-162）仅出现在糖尿病大鼠晶状体中，表明糖尿病中m-钙蛋白酶的特异性激活。α B-晶状体蛋白只有一个C-末端截短的组分，α B（1-170），其在糖尿病中也显示出增加的水平。结论：这些数据表明，糖尿病应激导致酶或非酶切割特定的C-末端氨基酸残基之间的肽键。这种截短的α-晶状体蛋白似乎有助于增加通常存在于糖尿病晶状体中的α H级分的水平。α A-晶状体蛋白伴侣活性的丧失似乎与C-末端氨基酸残基的截短有关。
PURPOSE To investigate the influence of diabetes on the cleavage of C-terminal amino acid residues of alphaA- and alphaB-crystallins in human and rat lenses. METHODS The human lenses were diabetic or age-matched control lenses from donors 57, 59, 69, and 72 years of age. Lenses were also obtained from streptozotocin-induced diabetic rats. Individual lens crystallins in water-soluble fractions were separated by gel-permeation chromatography. The high (alphaH)- and low (alphaL)-molecular-weight fractions were analyzed by electrospray ionization mass spectrometry. RESULTS A typical mass spectrum of alphaA-crystallin from human lenses showed intact unmodified alphaA-crystallin, truncated alphaA(1-172), and monophosphorylated alphaA-crystallin. Diabetic lenses showed nearly twofold higher levels of alphaA(1-172) than did the control lenses. Also, the alphaH fraction consistently showed significantly higher levels of alphaA(1-172) than the alphaL fraction. Human alphaB-crystallin showed no evidence of C-terminal truncation. Rat alphaA-crystallin had five C-terminal-truncated components, most of which showed substantial increases in diabetes. Truncated alphaA(1-162) appeared only in the diabetic rat lenses, suggesting specific activation of m-calpain in diabetes. alphaB-crystallin had only one C-terminal-truncated component, alphaB(1-170), which also showed increased levels in diabetes. CONCLUSIONS These data suggest that diabetic stress causes either enzymatic or nonenzymatic cleavage of peptide bonds between specific C-terminal amino acid residues. Such truncated alpha-crystallins appear to contribute to an increased level of the alphaH fraction generally present in diabetic lenses. Loss of alphaA-crystallin chaperone activity seems to be related to truncation of the C-terminal amino acid residues.