Lee H C, Aarhus R
Department of Physiology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Biol Chem. 1997 Aug 15;272(33):20378-83. doi: 10.1074/jbc.272.33.20378.
Nicotinic acid adenine dinucleotide phosphate (NAADP) mobilizes Ca2+ through a mechanism totally independent of cyclic ADP-ribose or inositol trisphosphate. The structural determinants important for its Ca2+ release activity were investigated using a series of analogs. It is shown that changing the 3-carboxyl group of the nicotinic acid (NA) moiety in NAADP to either an uncharged carbinol or from the 3-position to the 4-position of the pyridine ring totally eliminates the Ca2+ release activity. Conversion of the 3-carboxyl to other negatively charged groups, either 3-sulfonate, 3-acetate, or 3-quinoline carboxylate, retains the Ca2+ release activity, although their half-maximal effective concentrations (EC50) are 100-200-fold higher. Changing the 6-amino group of the adenine to a hydroxyl group results in more than a 1000-fold decrease in the Ca2+ release activity. Conversion of the 2'-phosphate to 2',3'-cyclic phosphate or 3'-phosphate likewise increases the EC50 by about 5- and 20-fold, respectively. Similar to NAADP, all of the active analogs can also desensitize the Ca2+ release mechanism at subthreshold concentrations, suggesting that this novel property is intrinsic to the release mechanism. The series of analogs used was produced by using ADP-ribosyl cyclase to catalyze the exchange of the nicotinamide group of various analogs of NADP with various analogs of NA. An important determinant in NA that is crucial to the base exchange reaction was shown to be the 2-position of the pyridine ring. Neither pyridine-2-carboxylate nor 2-methyl-NA support the exchange reaction. The negative charge and the position of the 3-carboxyl group are nonessential since both pyridine-3-carbinol and pyridine-4-carboxylate support the base exchange reaction. In addition to the information on the structure-activity relationships of NAADP and NA, this study also demonstrates the utility of the base exchange reaction as a general approach for synthesizing NAADP analogs.
烟酰胺腺嘌呤二核苷酸磷酸（NAADP）通过一种完全独立于环ADP - 核糖或肌醇三磷酸的机制来动员钙离子（Ca2+）。我们使用一系列类似物研究了对其Ca2+释放活性重要的结构决定因素。结果表明，将NAADP中烟酸（NA）部分的3 - 羧基改为不带电荷的甲醇，或者将吡啶环的3位改为4位，会完全消除Ca2+释放活性。将3 - 羧基转化为其他带负电荷的基团，如3 - 磺酸基、3 - 乙酸基或3 - 喹啉羧酸基，虽然它们的半数有效浓度（EC50）高100 - 200倍，但仍保留Ca2+释放活性。将腺嘌呤的6 - 氨基改为羟基会导致Ca2+释放活性降低1000倍以上。将2'-磷酸转化为2',3'-环磷酸或3'-磷酸同样会使EC50分别增加约5倍和20倍。与NAADP类似，所有活性类似物在亚阈值浓度下也能使Ca2+释放机制脱敏，这表明这种新特性是释放机制所固有的。所使用的一系列类似物是通过使用ADP - 核糖基环化酶催化NADP的各种类似物的烟酰胺基团与NA的各种类似物进行交换而产生的。结果表明，NA中对碱基交换反应至关重要的一个重要决定因素是吡啶环的2位。吡啶 - 2 - 羧酸酯和2 - 甲基 - NA都不支持交换反应。3 - 羧基的负电荷和位置并非必需，因为吡啶 - 3 - 甲醇和吡啶 - 4 - 羧酸酯都支持碱基交换反应。除了关于NAADP和NA的构效关系的信息外，本研究还证明了碱基交换反应作为合成NAADP类似物的通用方法的实用性。
