Biozentrum, University of Basel, Basel, Switzerland.
Center for Molecular Modeling, Ghent University, Zwijnaarde, Belgium.
Nat Commun. 2022 Feb 23;13(1):1022. doi: 10.1038/s41467-022-28361-1.
Transport of lipids across membranes is fundamental for diverse biological pathways in cells. Multiple ion-coupled transporters take part in lipid translocation, but their mechanisms remain largely unknown. Major facilitator superfamily (MFS) lipid transporters play central roles in cell wall synthesis, brain development and function, lipids recycling, and cell signaling. Recent structures of MFS lipid transporters revealed overlapping architectural features pointing towards a common mechanism. Here we used cysteine disulfide trapping, molecular dynamics simulations, mutagenesis analysis, and transport assays in vitro and in vivo, to investigate the mechanism of LtaA, a proton-dependent MFS lipid transporter essential for lipoteichoic acid synthesis in the pathogen Staphylococcus aureus. We reveal that LtaA displays asymmetric lateral openings with distinct functional relevance and that cycling through outward- and inward-facing conformations is essential for transport activity. We demonstrate that while the entire amphipathic central cavity of LtaA contributes to lipid binding, its hydrophilic pocket dictates substrate specificity. We propose that LtaA catalyzes lipid translocation by a 'trap-and-flip' mechanism that might be shared among MFS lipid transporters.
跨膜脂质运输是细胞内多种生物途径的基础。多种离子偶联转运体参与脂质易位，但它们的机制在很大程度上仍不清楚。主要易化因子超家族（MFS）脂质转运体在细胞壁合成、大脑发育和功能、脂质回收以及细胞信号转导中发挥核心作用。最近的 MFS 脂质转运体结构揭示了重叠的结构特征，指向一个共同的机制。在这里，我们使用半胱氨酸二硫键捕获、分子动力学模拟、突变分析以及体外和体内的转运实验，研究了 LtaA 的机制，LtaA 是一种质子依赖的 MFS 脂质转运体，对于病原体金黄色葡萄球菌中脂磷壁酸的合成至关重要。我们揭示了 LtaA 显示出不对称的侧向开口，具有不同的功能相关性，并且向外和向内构象的循环对于转运活性至关重要。我们证明，虽然 LtaA 的整个两亲性中央腔都有助于脂质结合，但它的亲水口袋决定了底物特异性。我们提出 LtaA 通过“捕获-翻转”机制催化脂质易位，该机制可能在 MFS 脂质转运体中共享。
