Janssen Edwin, Kuiper Jan, Hodgson Denice, Zingman Leonid V, Alekseev Alexey E, Terzic Andre, Wieringa Bé
Department of Cell Biology, NCMLS University Medical Center, University of Nijmegen, the Netherlands.
Mol Cell Biochem. 2004 Jan-Feb;256-257(1-2):59-72. doi: 10.1023/b:mcbi.0000009859.15267.db.
Adenylate kinases (AK, EC 2.7.4.3) have been considered important enzymes for energy homeostasis and metabolic signaling. To gain a better understanding of their cell-specific significance we studied the structural and functional aspects of products of one adenylate kinase gene, AK1, in mouse tissues. By combined computer database comparison and Northern analysis of mRNAs, we identified transcripts of 0.7 and 2.0 kilobases with different 5' and 3' non-coding regions which result from alternative use of promoters and polyadenylation sites. These mRNAs specify two distinct proteins, AK1 and a membrane-bound AK1 isoform (AK1beta), which differ in their N-terminal end and are co-expressed in several tissues with high-energy demand, including the brain. Immunohistochemical analysis of brain tissue and primary neurons and astrocytes in culture demonstrated that AK1 isoforms are expressed predominantly in neurons. AK1beta, when tested in transfected COS-1 and N2a neuroblastoma cells, located at the cellular membrane and was able to catalyze phosphorylation of ADP in vitro. In addition, AK1beta mediated AMP-induced activation of recombinant ATP-sensitive potassium channels in the presence of ATP. Thus, two structurally distinct AK1 isoforms co-exist in the mouse brain within distinct cellular locations. These enzymes may function in promoting energy homeostasis in the compartmentalized cytosol and in translating cellular energetic signals to membrane metabolic sensors.
腺苷酸激酶（AK，EC 2.7.4.3）被认为是能量稳态和代谢信号传导的重要酶。为了更好地理解它们在细胞特异性方面的意义，我们研究了小鼠组织中一个腺苷酸激酶基因AK1产物的结构和功能。通过计算机数据库比较和mRNA的Northern分析相结合，我们鉴定出了0.7和2.0千碱基的转录本，它们具有不同的5'和3'非编码区，这是由于启动子和聚腺苷酸化位点的交替使用所致。这些mRNA编码两种不同的蛋白质，AK1和一种膜结合的AK1同工型（AK1β），它们的N末端不同，并且在包括大脑在内的几种高能量需求组织中共同表达。对脑组织以及培养的原代神经元和星形胶质细胞的免疫组织化学分析表明，AK1同工型主要在神经元中表达。在转染的COS-1和N2a神经母细胞瘤细胞中进行测试时，AK1β定位于细胞膜，并且能够在体外催化ADP的磷酸化。此外，在ATP存在的情况下，AK1β介导了AMP诱导的重组ATP敏感性钾通道的激活。因此，两种结构不同的AK1同工型在小鼠大脑的不同细胞位置中共存。这些酶可能在促进分隔的胞质溶胶中的能量稳态以及将细胞能量信号转化为膜代谢传感器方面发挥作用。
