Bikle D, Munson S, Christakos S, Kumar R, Buckendahl P
Department of Medicine, Veterans Administration Medical Center, San Francisco, CA 94121.
Biochim Biophys Acta. 1989 Jan 17;1010(1):122-7. doi: 10.1016/0167-4889(89)90192-4.
The intestinal brush-border membrane contains a high concentration of calmodulin bound to a 105,000 dalton (105 kDa) protein. Binding of radioiodinated calmodulin to this protein does not require calcium but is inhibited by trifluoperazine and excess unlabelled calmodulin. Recent evidence suggests that the 105 kDa protein in conjunction with calmodulin may be involved in the regulation of calcium transport across the brush-border membrane. In this report, we evaluated the binding of the 105 kDa protein to other radioiodinated calcium-binding proteins including the vitamin D-dependent intestinal calcium-binding protein. We observed that troponin C and S100 beta protein both bound strongly to the 105 kDa protein. The binding of S100 beta was inhibited by EGTA, but was little affected by trifluoperazine and excess unlabelled S100 beta, whereas that of troponin C was inhibited by trifluoperazine and excess unlabelled troponin C, but was little affected by EGTA. Both troponin C and S100 beta bound to a large number of proteins to which calmodulin did not bind. The vitamin D-dependent calcium-binding protein (calbindin) from chick intestine and rat kidney also bound to the 105 kDa protein, albeit more weakly than troponin C, S100 beta and calmodulin. The binding of the calbindins was increased by EGTA and was little affected by trifluoperazine and excess unlabelled calbindin. Parvalbumin, rat osteocalcin, and alpha-lactalbumin showed little binding to any brush-border membrane protein. Our results indicate that the 105 kDa calmodulin-binding protein of the intestinal brush border can bind to a variety of calcium-binding proteins all of which contain homologous regions thought to be the calcium-binding sites. Only the binding of troponin C resembles the binding of calmodulin, however, in being inhibited by trifluoperazine and excess unlabelled ligand. The functional significance of these observations in terms of regulating calcium transport across the brush-border membrane remains to be established.
肠刷状缘膜含有高浓度的钙调蛋白，它与一种105,000道尔顿（105 kDa）的蛋白质结合。放射性碘化钙调蛋白与该蛋白质的结合不需要钙，但会受到三氟拉嗪和过量未标记钙调蛋白的抑制。最近的证据表明，105 kDa的蛋白质与钙调蛋白一起可能参与了跨刷状缘膜的钙转运调节。在本报告中，我们评估了105 kDa蛋白质与其他放射性碘化钙结合蛋白的结合情况，包括维生素D依赖性肠钙结合蛋白。我们观察到肌钙蛋白C和S100β蛋白都与105 kDa蛋白质强烈结合。S100β的结合受到乙二醇双四乙酸（EGTA）的抑制，但几乎不受三氟拉嗪和过量未标记S100β的影响，而肌钙蛋白C的结合受到三氟拉嗪和过量未标记肌钙蛋白C的抑制，但几乎不受EGTA的影响。肌钙蛋白C和S100β都与大量钙调蛋白不结合的蛋白质结合。来自鸡肠和大鼠肾脏的维生素D依赖性钙结合蛋白（钙结合蛋白）也与105 kDa蛋白质结合，尽管比肌钙蛋白C、S100β和钙调蛋白弱。钙结合蛋白的结合因EGTA而增加，几乎不受三氟拉嗪和过量未标记钙结合蛋白的影响。小清蛋白、大鼠骨钙素和α-乳白蛋白与任何刷状缘膜蛋白的结合都很少。我们的结果表明，肠刷状缘的105 kDa钙调蛋白结合蛋白可以与多种钙结合蛋白结合，所有这些钙结合蛋白都含有被认为是钙结合位点的同源区域。然而，只有肌钙蛋白C的结合类似于钙调蛋白的结合，即受到三氟拉嗪和过量未标记配体的抑制。这些观察结果在调节跨刷状缘膜的钙转运方面的功能意义仍有待确定。
