Maekawa S, Murofushi H, Nakamura S
Graduate School, Division of Science, University of Tokyo, Japan.
J Biol Chem. 1994 Jul 29;269(30):19462-5.
NAP-22, a recently identified neural tissue-enriched acidic protein, was shown to be a substrate of protein kinase C in vitro. Its phosphorylation site was assigned as Ser6 using deleted mutants expressed in Escherichia coli. Calmodulin inhibited this phosphorylation reaction. This inhibitory effect of calmodulin was dose-dependent and much stronger than its inhibitory effect to the phosphorylation of neuromodulin (GAP-43) with protein kinase C. The dissociation constant of NAP-22 and calmodulin obtained using the fluorescence change of dansyl-labeled calmodulin was much lower than that of neuromodulin and calmodulin. The phosphorylation of NAP-22 inhibited the association with calmodulin.
NAP-22是一种最近发现的富含神经组织的酸性蛋白，在体外被证明是蛋白激酶C的底物。利用在大肠杆菌中表达的缺失突变体，其磷酸化位点被确定为Ser6。钙调蛋白抑制了这种磷酸化反应。钙调蛋白的这种抑制作用具有剂量依赖性，且比其对蛋白激酶C介导的神经调节蛋白（GAP-43）磷酸化的抑制作用要强得多。利用丹磺酰化钙调蛋白的荧光变化测得的NAP-22与钙调蛋白的解离常数远低于神经调节蛋白与钙调蛋白的解离常数。NAP-22的磷酸化抑制了其与钙调蛋白的结合。
