Mereish K A, Solow R, Bunner D L, Fajer A B
Medical Division Research Laboratory, U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, MD 21702-5011.
Pept Res. 1990 Sep-Oct;3(5):233-7.
A variety of small peptides bind calmodulin (CaM) and inhibit CaM-dependent enzyme activity. The cyclic peptides cyclosporin A (CSA) and gramicidin-S (GRS) are shown to bind CaM and inhibit 3',5'-cyclic nucleotide phosphodiesterase (PDE) in a calcium-dependent manner. The cyclic peptide microcystin-LR (MLR) and the depsipeptides, valinomycin (VLM) and enniatin-B (ENB), bind to CaM and inhibit PDE activity. Spectral changes exhibited by the binding of MLR, VLM and ENB to dansyl-CaM as compared to that of CSA and GRS reflected different binding sites and/or different conformational changes. The apparent binding constants (Kd) for CaM-peptide were estimated and found to be 4.8 microM for CSA, 2.85 microM GRS, 12.99 microM MLR, 4.29 microM VLM and 41.26 microM ENB. Although these peptides did not inhibit baseline PDE activity, they did inhibit CaM-dependent PDE activity in a dose-dependent manner. Half-maximal inhibition (IC50) of PDE occurred approximately at 0.11 microM MLR; 0.45 microM GRS; and greater than 5 microM for ENB, CSA and VLM. This may be the first observation that these peptides (MLR, VLM and ENB) bind to a known cytoplasmic protein and inhibit an enzyme system dependent on that protein for optimal activity. Interaction of these peptides with CaM may be responsible for creating conformational-functional changes in CaM, thus altering the signal transduction mechanism required for CaM-dependent enzymes, such as cyclic nucleotidase, protein kinases and phospholipase A2.
多种小肽可结合钙调蛋白（CaM）并抑制CaM依赖性酶活性。已表明环孢菌素A（CSA）和短杆菌肽-S（GRS）这两种环肽以钙依赖性方式结合CaM并抑制3'，5'-环核苷酸磷酸二酯酶（PDE）。环肽微囊藻毒素-LR（MLR）以及缩肽缬氨霉素（VLM）和恩镰孢菌素-B（ENB）可结合CaM并抑制PDE活性。与CSA和GRS相比，MLR、VLM和ENB与丹磺酰-CaM结合所表现出的光谱变化反映了不同的结合位点和/或不同的构象变化。估算了CaM-肽的表观结合常数（Kd），发现CSA为4.8 microM，GRS为2.85 microM，MLR为12.99 microM，VLM为4.29 microM，ENB为41.26 microM。尽管这些肽不抑制基础PDE活性，但它们确实以剂量依赖性方式抑制CaM依赖性PDE活性。PDE的半数最大抑制（IC50）大约出现在0.11 microM MLR；0.45 microM GRS；而对于ENB、CSA和VLM则大于5 microM。这可能是首次观察到这些肽（MLR、VLM和ENB）与一种已知的细胞质蛋白结合并抑制依赖该蛋白以实现最佳活性的酶系统。这些肽与CaM的相互作用可能导致CaM发生构象-功能变化，从而改变CaM依赖性酶（如环核苷酸酶、蛋白激酶和磷脂酶A2）所需的信号转导机制。
