Abstract：
ABCA4 is an ATP-binding cassette (ABC) transporter that prevents the buildup of toxic retinoid compounds by facilitating the transport of N-retinylidene-phosphatidylethanolamine across membranes of rod and cone photoreceptor cells. Over 1500 missense mutations in ABCA4, many in the nucleotide-binding domains (NBDs), have been genetically linked to Stargardt disease. Here, we show by cryo-EM that ABCA4 is converted from an open outward conformation to a closed conformation upon the binding of adenylyl-imidodiphosphate. Structural information and biochemical studies were used to further define the role of the NBDs in the functional properties of ABCA4 and the mechanisms by which mutations lead to the loss in activity. We show that ATPase activity in both NBDs is required for the functional activity of ABCA4. Mutations in Walker A asparagine residues cause a severe reduction in substrate-activated ATPase activity due to the loss in polar interactions with residues within the D-loops of the opposing NBD. The structural basis for how disease mutations in other NBD residues, including the R1108C, R2077W, R2107H, and L2027F, affect the structure and function of ABCA4 is described. Collectively, our studies provide insight into the structure and function of ABCA4 and mechanisms underlying Stargardt disease.
摘要：
ABCA4是一种ATP结合盒（ABC）转运蛋白，可通过促进N-视黄亚烷基磷脂酰乙醇胺跨视杆和视锥感光细胞膜的转运来防止有毒的类视黄醇化合物的积聚。ABCA4中超过1500个错义突变，许多在核苷酸结合域（NBD）中，与Stargardt病（STGD1）有遗传联系。这里,我们通过低温电子显微镜显示，ABCA4在AMP-PNP结合后从开放的向外构象转化为封闭构象。结构信息和生化研究用于进一步定义NBD在ABCA4功能特性中的作用以及突变导致活性丧失的机制。我们表明，ABCA4的功能活性需要两个NBD中的ATPase活性。WalkerA天冬酰胺残基的突变导致底物激活的ATPase活性严重降低，这是由于与相对NBD的D环内残基的极性相互作用丧失。包括R1108C在内的其他NBD残基中的疾病突变的结构基础，R2077W,R2107H和L2027F对ABCA4的构造和功效影响停止了描写。总的来说，我们的研究为ABCA4的结构和功能以及STGD1的潜在机制提供了见解.
