Fatty acid (FA) transfer proteins extract FA from membranes and sequester their ligand to facilitate its movement through the cytosol. While detailed views of soluble protein-FA complexes are available, how FA exchange occurs at the membrane has remained unknown. Staphylococcus aureus FakB1 is a prototypical bacterial FA transfer protein that binds palmitate within a narrow, buried tunnel. Here, we determine the conformational change from this closed state to an open state that engages the phospholipid bilayer. Upon membrane binding, a dynamic loop in FakB1 that covers the FA binding site disengages and folds into an amphipathic helix. This helix inserts below the phosphate plane of the bilayer to create a diffusion channel for the FA to exchange between the protein and the membrane. The structure of the bilayer-associated conformation of FakB1 has local similarities with mammalian FA binding proteins and provides a general conceptual framework for how these proteins interact with the membrane to promote lipid transfer.

中文翻译：

---

允许配体进入和退出细菌脂肪酸结合蛋白的结构转变

脂肪酸 (FA) 转移蛋白从膜中提取 FA 并隔离其配体以促进其通过细胞质的运动。虽然可以获得可溶性蛋白质-FA 复合物的详细视图，但 FA 交换如何在膜上发生仍然未知。金黄色葡萄球菌FakB1 是一种原型细菌 FA 转移蛋白，可在狭窄的埋藏隧道内结合棕榈酸酯。在这里，我们确定了从这种闭合状态到与磷脂双层结合的开放状态的构象变化。膜结合后，FakB1 中覆盖 FA 结合位点的动态环脱离并折叠成两亲螺旋。该螺旋插入双层磷酸盐平面下方，为 FA 在蛋白质和膜之间交换创建扩散通道。FakB1 的双层相关构象的结构与哺乳动物 FA 结合蛋白具有局部相似性，并为这些蛋白质如何与膜相互作用以促进脂质转移提供了一般概念框架。