The University of Pittsburgh, Pulmonary, Allergy, & Critical Care Medicine, UPMC Montefiore, NW 628, Department of Medicine, Pittsburgh, PA 15213, USA.
Mol Cell Biol. 2011 May;31(9):1905-20. doi: 10.1128/MCB.00723-10. Epub 2011 Feb 22.
Calmodulin is a universal calcium-sensing protein that has pleiotropic effects. Here we show that calmodulin inhibits a new SCF (Skp1-Cullin-F-box) E3 ligase component, FBXL2. During Pseudomonas aeruginosa infection, SCF (FBXL2) targets the key enzyme, CCTα, for its monoubiquitination and degradation, thereby reducing synthesis of the indispensable membrane and surfactant component, phosphatidylcholine. P. aeruginosa triggers calcium influx and calcium-dependent activation of FBXL2 within the Golgi complex, where it engages CCTα. FBXL2 through its C terminus binds to the CCTα IQ motif. FBXL2 knockdown increases CCTα levels and phospholipid synthesis. The molecular interaction of FBXL2 with CCTα is opposed by calmodulin, which traffics to the Golgi complex, binds FBXL2 (residues 80 to 90) via its C terminus, and vies with the ligase for occupancy within the IQ motif. These observations were recapitulated in murine models of P. aeruginosa-induced surfactant deficiency, where calmodulin gene transfer reduced FBXL2 actions by stabilizing CCTα and lessening the severity of inflammatory lung injury. The results provide a unique model of calcium-regulated intermolecular competition between an E3 ligase subunit and an antagonist that is critically relevant to pneumonia and lipid homeostasis.
钙调蛋白是一种普遍存在的钙感应蛋白，具有多种效应。在这里，我们表明钙调蛋白抑制了一种新的 SCF（Skp1-Cullin-F-box）E3 连接酶成分 FBXL2。在铜绿假单胞菌感染过程中，SCF（FBXL2）将关键酶 CCTα 作为其单泛素化和降解的靶标，从而减少必需膜和表面活性剂成分磷脂酰胆碱的合成。铜绿假单胞菌触发钙内流和钙依赖性 FBXL2 在高尔基体复合物中的激活，在那里它与 CCTα 结合。FBXL2 通过其 C 端与 CCTα 的 IQ 基序结合。FBXL2 敲低会增加 CCTα 水平和磷脂合成。钙调蛋白与 CCTα 的分子相互作用与 FBXL2 相反，钙调蛋白在高尔基体中运输，通过其 C 端与 FBXL2（残基 80 至 90）结合，并与 IQ 基序内的连接酶竞争占据。这些观察结果在铜绿假单胞菌诱导的表面活性剂缺乏症的小鼠模型中得到了再现，其中钙调蛋白基因转移通过稳定 CCTα 和减轻炎症性肺损伤的严重程度来减少 FBXL2 的作用。这些结果提供了一个独特的钙调节 E3 连接酶亚基和拮抗剂之间的分子间竞争模型，这与肺炎和脂质动态平衡密切相关。
