Cohen B E, Lee G, Arispe N, Pollard H B
Laboratory of Cell Biology and Genetics, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
FEBS Lett. 1995 Dec 27;377(3):444-50. doi: 10.1016/0014-5793(95)01395-4.
The annexin (Anx) gene family comprises a set of calcium-dependent membrane binding proteins, which have been implicated in a wide variety of cellular processes including membrane fusion and calcium channel activity. We report here that cAMP activates Ca(2+)-dependent aggregation of both phosphatidylserine (PS) liposomes and bovine chromaffin granules driven by [des 1-12]annexin I (lipocortin I, Anx1). The mechanism of cAMP action involves an increase in AnxI-dependent cooperativity on the rate of such a reaction without affecting the corresponding k1/2 values. Cyclic AMP causes the values of the Hill coefficient (nH) for AnxI to change from 3 to 6 in both PS liposomes and chromaffin granules. By contrast, ATP inhibits the rate of aggregation activity without affecting the cooperativity or the extent of aggregation process. We were also able to photolabel Anx1 specifically with an 8-azido analogue of cAMP by a calcium-independent process. Such a process is saturable, yielding a Kd = 0.8 microM by Scatchard analysis. Specific displacement occurs in the presence of cAMP and ATP. Finally, we found that cAMP alters the conductance of calcium channels formed by AnxI in planar lipid bilayers. We interpret these data to indicate that AnxI binds both calcium and cAMP independently, and that both actions have functional consequences. This is the first report of a nucleotide binding function for a member of the annexin gene family.
膜联蛋白（Anx）基因家族由一组钙依赖性膜结合蛋白组成，这些蛋白参与了包括膜融合和钙通道活性在内的多种细胞过程。我们在此报告，环磷酸腺苷（cAMP）可激活由[去1-12]膜联蛋白I（脂皮质素I，Anx1）驱动的磷脂酰丝氨酸（PS）脂质体和牛嗜铬颗粒的钙依赖性聚集。cAMP的作用机制涉及增加AnxI对这种反应速率的依赖性协同作用，而不影响相应的k1/2值。环磷酸腺苷使PS脂质体和嗜铬颗粒中AnxI的希尔系数（nH）值从3变为6。相比之下，三磷酸腺苷（ATP）抑制聚集活性的速率，但不影响协同作用或聚集过程的程度。我们还能够通过一个不依赖钙的过程用cAMP的8-叠氮类似物特异性地光标记Anx1。这样的过程是可饱和的，通过Scatchard分析得出解离常数（Kd）=0.8微摩尔。在存在cAMP和ATP的情况下会发生特异性置换。最后，我们发现cAMP改变了由AnxI在平面脂质双分子层中形成的钙通道的电导率。我们对这些数据的解释是，AnxI独立地结合钙和cAMP，并且这两种作用都有功能后果。这是膜联蛋白基因家族成员核苷酸结合功能的首次报道。
