Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada.
Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, BC, Canada.
Nat Commun. 2021 Oct 8;12(1):5902. doi: 10.1038/s41467-021-26161-7.
ABCA4 is an ATP-binding cassette (ABC) transporter that flips N-retinylidene-phosphatidylethanolamine (N-Ret-PE) from the lumen to the cytoplasmic leaflet of photoreceptor membranes. Loss-of-function mutations cause Stargardt disease (STGD1), a macular dystrophy associated with severe vision loss. To define the mechanisms underlying substrate binding and STGD1, we determine the cryo-EM structure of ABCA4 in its substrate-free and bound states. The two structures are similar and delineate an elongated protein with the two transmembrane domains (TMD) forming an outward facing conformation, extended and twisted exocytoplasmic domains (ECD), and closely opposed nucleotide binding domains. N-Ret-PE is wedged between the two TMDs and a loop from ECD1 within the lumen leaflet consistent with a lateral access mechanism and is stabilized through hydrophobic and ionic interactions with residues from the TMDs and ECDs. Our studies provide a framework for further elucidating the molecular mechanism associated with lipid transport and disease and developing promising disease interventions.
ABCA4 是一种 ATP 结合盒（ABC）转运蛋白，可将 N-视黄基磷酰乙醇胺（N-Ret-PE）从腔室翻转到光感受器膜的细胞质小叶。功能丧失突变会导致 Stargardt 病（STGD1），这是一种与严重视力丧失相关的黄斑营养不良。为了定义底物结合和 STGD1 的机制，我们确定了无底物和结合状态下 ABCA4 的冷冻电镜结构。这两个结构相似，描绘了一个长形蛋白，其中两个跨膜结构域（TMD）形成向外的构象，延伸和扭曲的胞外结构域（ECD），以及紧密相对的核苷酸结合结构域。N-Ret-PE 位于两个 TMD 之间，ECD1 中的一个环位于腔室小叶内，这与侧向进入机制一致，并通过与 TMD 和 ECD 中的残基的疏水和离子相互作用得到稳定。我们的研究为进一步阐明与脂质转运和疾病相关的分子机制以及开发有前途的疾病干预措施提供了框架。
