Ca2(+)-induced conformational change and aggregation of chromogranin A.
Ca2(+)-induced conformational change and aggregation of chromogranin A.
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DOI：
10.1016/s0021-9258(18)77318-3
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发表时间：
1990-08
期刊：
影响因子：
--
通讯作者：
S. Yoo;J. Albanesi
中科院分区：
文献类型：
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作者：
S. Yoo;J. Albanesi
嗜铬蛋白A是牛肾上腺嗜铬颗粒中最丰富的蛋白质，它以Ca2+依赖性方式结合钙调蛋白，利用钙调蛋白结合特性来纯化嗜铬蛋白A。嗜铬蛋白A在过去被描述为一种“无规螺旋多肽”，几乎没有α螺旋或β折叠构象。然而，使用纯天然嗜铬粒蛋白 A 进行的圆二色性测量显示出相对较高的 α 螺旋含量（囊泡内 pH 值为 5.5 时为 40%）。荧光研究证实了之前的观察结果，即嗜铬粒蛋白 A 以低亲和力结合 Ca2+。考虑到分泌囊泡中Ca2+浓度较高，考察了Ca2+对嗜铬粒蛋白A二级结构和自缔合的影响。在 pH 5.5 时，Ca2+ 诱导嗜铬粒蛋白 A 的 α 螺旋度从 40% 降低至 30%。相比之下，在 pH 7.5 下，等量的 Ca2+ 使蛋白质的 α 螺旋度从 25% 增加到 40%。肾上腺提取物的煮沸是嗜铬粒蛋白 A 的常用纯化方法，可分离出构象不同的嗜铬粒蛋白 A 分子。与甲状旁腺的分泌蛋白 I 不同（Gorr, S.-V.、Dean, W. L.、Radley, T. L. 和 Cohn, D. V. (1988) Bone Mineral 4, 17-25），嗜铬粒蛋白 A 在 Ca2+ 存在下快速聚集。聚集的程度和速率高度依赖于Ca2+浓度。尽管pH 7.5 下的聚集速率和程度均远低于pH 5.5 下的聚集，但嗜铬粒蛋白A 的聚集在两种pH 下均进行。在这方面，嗜铬粒蛋白 A 与人嗜铬粒蛋白 C 不同，Gerdes 等人证明了这一点。 （Gerdes, H.-H.、Rosa, P.、Phillips, E.、Baeuerle, P. A.、Frank, R.、Argos, P. 和 Huttner, W. B. (1989) J. Biol. Chem. 264, 12009-12015）在 pH 5.2 时聚集，但在 pH 7.4 时不聚集。
Chromogranin A, the most abundant protein in bovine adrenal chromaffin granules, bound calmodulin in a Ca2(+)-dependent manner, and the calmodulin-binding property was utilized to purify chromogranin A. Chromogranin A has been described in the past as a “random-coil polypeptide” with little alpha-helix or beta-sheet conformation. However, circular dichroism measurements with pure, native chromogranin A revealed relatively high alpha-helical contents (40% at the intravesicular pH of 5.5). Fluorescence studies confirmed previous observations that chromogranin A binds Ca2+ with low affinity. Considering the high concentration of Ca2+ in the secretory vesicle, the effect of Ca2+ on the secondary structure and self-association of chromogranin A was examined. Ca2+ induced a decrease of alpha-helicity of chromogranin A from 40 to 30% at pH 5.5. In contrast, at pH 7.5 the same amount of Ca2+ increased alpha-helicity of the protein from 25 to 40%. Boiling of the adrenal extract, a commonly used purification procedure for chromogranin A, resulted in the isolation of conformationally distinct chromogranin A molecule. Unlike secretory protein-I of the parathyroid gland (Gorr, S.-V., Dean, W. L., Radley, T. L., and Cohn, D. V. (1988) Bone Mineral 4, 17-25), chromogranin A aggregated rapidly in the presence of Ca2+. The extent and rate of aggregation were highly dependent on Ca2+ concentration. Although both the rate and extent of aggregation at pH 7.5 were much lower than those at pH 5.5, aggregation of chromogranin A proceeded at both pH's. In this respect, chromogranin A differs from human chromogranin C which was shown by Gerdes et al. (Gerdes, H.-H., Rosa, P., Phillips, E., Baeuerle, P. A., Frank, R., Argos, P., and Huttner, W. B. (1989) J. Biol. Chem. 264, 12009-12015) to aggregate at pH 5.2 but not at pH 7.4.