Pittman J K, Hirschi K D
Plant Physiology Group, U.S. Department of Agriculture/Agricultural Research Service, Baylor College of Medicine, 1100 Bates Street, Houston, TX 77030, USA.
Plant Physiol. 2001 Nov;127(3):1020-9.
Regulation of Ca(2+) transport determines the duration of a Ca(2+) signal, and hence, the nature of the biological response. Ca(2+)/H+ antiporters such as CAX1 (cation exchanger 1), play a key role in determining cytosolic Ca(2+) levels. Analysis of a full-length CAX1 clone suggested that the CAX1 open reading frame contains an additional 36 amino acids at the N terminus that were not found in the original clone identified by suppression of yeast (Saccharomyces cerevisiae) vacuolar Ca(2+) transport mutants. The long CAX1 (lCAX1) could not suppress the yeast Ca(2+) transport defects despite localization to the yeast vacuole. Calmodulin could not stimulate lCAX1 Ca(2+)/H+ transport in yeast; however, minor alterations in the 36-amino acid region restored Ca(2+)/H+ transport. Sequence analysis suggests that a 36-amino acid N-terminal regulatory domain may be present in all Arabidopsis CAX-like genes. Together, these results suggest a structural feature involved in regulation of Ca(2+)/H+ antiport.
Ca(2+)转运的调节决定了Ca(2+)信号的持续时间，进而决定了生物反应的性质。Ca(2+)/H+反向转运蛋白，如CAX1（阳离子交换蛋白1），在决定胞质Ca(2+)水平方面起着关键作用。对全长CAX1克隆的分析表明，CAX1开放阅读框在N端含有另外36个氨基酸，而在通过抑制酵母（酿酒酵母）液泡Ca(2+)转运突变体鉴定的原始克隆中未发现这些氨基酸。尽管长CAX1（lCAX1）定位于酵母液泡，但它不能抑制酵母的Ca(2+)转运缺陷。钙调蛋白不能刺激酵母中的lCAX1 Ca(2+)/H+转运；然而，36个氨基酸区域的微小改变恢复了Ca(2+)/H+转运。序列分析表明，所有拟南芥CAX样基因中可能都存在一个36个氨基酸的N端调节结构域。这些结果共同表明了一个参与Ca(2+)/H+反向转运调节的结构特征。
