Chen Hongwen, Ha Hoa T T, Elghobashi-Meinhardt Nadia, Le Nhung A, Schmiege Philip, Nguyen Long N, Li Xiaochun
Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390.
Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119228.
Proc Natl Acad Sci U S A. 2025 Jan 7;122(1):e2409596121. doi: 10.1073/pnas.2409596121. Epub 2024 Dec 31.
Spns1 mediates the rate-limiting efflux of lysophospholipids from the lysosome to the cytosol. Deficiency of Spns1 is associated with embryonic senescence, as well as liver and skeletal muscle atrophy in animal models. However, the mechanisms by which Spns1 transports lysophospholipid and proton sensing remain unclear. Here, we present a cryogenic electron microscopy structure of human Spns1 in lysophosphatidylcholine (LPC)-bound lumen-facing conformation. Notably, LPC snugly binds within the luminal-open cavity, where the molecular dynamics simulations reveal that LPC presents a propensity to enter between transmembrane-helices (TM) 5 and 8. Structural comparisons and cell-based transport assays uncover several pivotal residues at TM 5/8 that orchestrate the transport cycle, which are unique to Spns1. Furthermore, we identify a five-residue network that is crucial for proton-sensing by Spns1. Transference of these network residues to Spns2, a sphingosine-1-phosphate uniporter, causes the chimeric Spns2 to be low pH dependent. Our results reveal molecular insights into lysosomal LPC transport and the proton-sensing mechanism by Spns1.
Spns1介导溶血磷脂从溶酶体到细胞质的限速外流。在动物模型中，Spns1的缺乏与胚胎衰老以及肝脏和骨骼肌萎缩有关。然而，Spns1转运溶血磷脂和质子感应的机制仍不清楚。在这里，我们展示了人Spns1在结合溶血磷脂酰胆碱（LPC）的面向内腔构象下的低温电子显微镜结构。值得注意的是，LPC紧密结合在内腔开放腔内，分子动力学模拟显示LPC倾向于进入跨膜螺旋（TM）5和8之间。结构比较和基于细胞的转运分析揭示了TM 5/8处几个协调转运循环的关键残基，这些残基是Spns1特有的。此外，我们确定了一个由五个残基组成的网络，它对Spns1的质子感应至关重要。将这些网络残基转移到鞘氨醇-1-磷酸单向转运体Spns2上，会使嵌合Spns2依赖低pH值。我们的结果揭示了溶酶体LPC转运和Spns1质子感应机制的分子见解。
