Hunziker W, Schrickel S
Central Research Units, Hoffmann-La Roche and Company, Ltd., Basle, Switzerland.
Mol Endocrinol. 1988 May;2(5):465-73. doi: 10.1210/mend-2-5-465.
Calbindin D28 cDNA clones were isolated from a rat brain library using a chicken intestinal Calbindin D28 cDNA probe. Nucleotide sequence analysis of these clones shows an open reading frame of 78 nucleotide coding for a 261 amino acid 29,994 dalton protein. The predicted amino acid sequence contains six repeats of a domain with the feature of an EF-hand calcium binding site. In domains II and VI, two of the five oxygen-containing amino acids important for the coordination of calcium are absent, suggesting that these two sites have lost their calcium-binding capability. Comparing the amino acid sequence to that recently reported for the chicken Calbindin D28 there is 79% homology. Tolerating conservative differences, the homology increases to 93%. Interestingly, domains II and VI which have presumably lost their calcium binding ability are very conserved among the two species (81% and 78%, respectively). Since an EF hand calcium binding site requires only certain types of amino acids at certain positions, rather than a specific amino acid sequence, maintaining a calcium binding site is a weak conservation pressure. To explain the high degree of homology of rat and chicken Calbindin D28, and in particular the conservation of the two degenerated domains over the 300 million years since divergence of birds and mammals, additional function(s) of the Calbindin D28 are postulated.
使用鸡肠钙结合蛋白D28 cDNA探针从大鼠脑文库中分离出钙结合蛋白D28 cDNA克隆。对这些克隆进行核苷酸序列分析，结果显示一个78个核苷酸的开放阅读框，编码一个含261个氨基酸、分子量为29,994道尔顿的蛋白质。预测的氨基酸序列包含一个具有EF-手型钙结合位点特征的结构域的六个重复序列。在结构域II和VI中，对于钙配位至关重要的五个含氧氨基酸中的两个缺失，这表明这两个位点已失去其钙结合能力。将该氨基酸序列与最近报道的鸡钙结合蛋白D28的氨基酸序列进行比较，发现同源性为79%。若考虑保守性差异，同源性则增至93%。有趣的是，推测已失去钙结合能力的结构域II和VI在这两个物种中非常保守（分别为81%和78%）。由于EF手型钙结合位点仅在特定位置需要某些类型的氨基酸，而非特定的氨基酸序列，因此维持钙结合位点的保守压力较小。为了解释大鼠和鸡的钙结合蛋白D28的高度同源性，尤其是自鸟类和哺乳动物分化以来的3亿年中这两个退化结构域的保守性，人们推测钙结合蛋白D28具有其他功能。
