铽离子发光探针研究pH诱导的植物钙调素构象变化

利用脱钙钙调素(apo-CaM),Tb.CaM和Ca.CaM系统的荧光光谱及酪氨酸-铽离子(Tyr-Tb3 )敏化荧光光谱,研究了pH诱导钙调素构象的改变.随着pH值的降低,apo-CaM的荧光强度下降并出现蓝移,Ca.CaM系统的荧光强度较Tb.CaM下降显著,Tyr-Tb3 敏化荧光光谱也有相当程度的降低.对荧光强度的变化与钙调素分子结构和构象的关系和pH诱导钙调素构象改变的机理作了详细的解释,H 可通过与Ca2 和Tb3 产生竞争结合,影响金属离子与钙调素的结合作用,还可以通过正电相斥或与肽链上带负电荷原子相结合而使CaM分子的极性增强,改变CaM表面的疏水性,降低CaM的活性.文章对pH诱导钙调素构象改变在胞外钙调素信号转导机制中的重要意义进行了阐述.

Study on the pH Induced Conformational Change of Plant CaM by Using Tb3+ Luminescence Probe

Calmodulin(CaM) is a ubiquitous Ca2 binding protein of eukaryotes,and regulates a broad spectrum of fundamental cellular processes.It has been established that CaM has both intracellular and extracellular signal transduction functions,but the mechanism of the fact that extracellullar CaM can be activated by Ca2 has been unclear.In order to establish the binding parameters of Ca2 to extracellular CaM at high Ca2 level and low pH,Tb3 fluorescence probe and fluorescence spectroscopy were used to investigate the influence of pH values on the conformational change of plant CaM.The fluorescence spectra in apo-CaM had blue shift and were quenched along with the change of pH value from 7.0 to 2.0.The fluorescence intensity of Ca-CaM system was remarkably lower than that of the Tb-CaM system and the Tyr-sensitized Tb3 fluorescence in Tb3 -CaM was quenched with the addition of H .On the basis of the results the relation between fluorescence intensity and conformational change of plant CaM and the mechanism of the changes in Tyr microenvironment induced by pH were discussed.It can be assumed that H can not only bind to CaM competiting with Ca2 or Tb3 but also alter the hydrophobic environment on the surface of CaM molecules,which may affect the activity of CaM.The study supports the extracellular CaM signal transduction mechanism significantly.