平滑肌肌球蛋白轻链激酶及ATP结合位点突变体对ATP酶活性的调节作用

目的：探寻MLCK的非激酶活性区域对MLCK活性的影响，进一步阐明MLCK的非激酶活性在调节平滑肌收缩过程中的分子机制。方法：利用编码MLCK全长的pColdI表达载体对其ATP结合位点进行定点突变，获得无激酶活性的MLCK突变体；应用Glycerol—PAGE鉴定肌球蛋白磷酸化水平；应用孔雀绿方法检测重组MLCK对肌球蛋白ATP酶活性的影响。结果：MLCK／△ATP（突变型）失去磷酸化肌球蛋白轻链的激酶活性；重组MLCK（野生型）和MLCK／AATP（突变型）均可以在非钙条件下激活非磷酸化肌球蛋白Mg2＋-ATP酶活性，抑制磷酸化肌球蛋白的Mg2＋．ATP酶活性，而且激活与抑制作用均随着MLCK浓度的增加而增大，但二者对肌球蛋白的ATP酶活性的作用没有显著差异（P〉0．05）。结论：平滑肌肌球蛋白轻链激酶及ATP结合位点突变体具有激活非磷酸化肌球蛋白ATP酶活性的作用。

Effect of Smooth Muscle Myosin Light Chain Kinase and the ATP Binding Site Mutant on ATPase Activity

Objective： To investigate the non-kinase activity of MLCK and to explain the molecular mechanismof its regulating in Smooth muscle contraction. Methods： The pCold I expression vector containing the cDNA of full length MLCK was used to get mutation and MLCK without the kinase activity were acquired. Glycerol-PAGE was used to confirm the phosphorylated myosin light chain. Marachite green method was used to examine the effect of recombinant full-length MLCKs on the phosphorylated and unphosphorylated myosin. Results： The MLCK/△ATP lost its kinase activity of phosphorylating myosin light chain. Both the wild type of recombinant MLCK and the MLCK/△ATP could activate the unphosphorylated myosin Mg2＋-ATPase activity and inhibit the phosphorylated myosin Mg2＋-ATPase activity in a dose dependent manner when there was no Ca2＋ existing. But there was no prominent difference between the wild type of recombinant MLCK and the MLCK/△ATP on the myosin ATPase activity （P〉0.05）. conclusions Both full-length smooth muscle myosin light chain kinase and its ATP binding site mutant could active unphosphorylated myosin ATPase activity.