Structural basis of receptor-mediated cellular vitamin A uptake

受体介导的细胞维生素 A 摄取的结构基础

• 批准号: 9898381
• 负责人: Filippo Mancia
• 金额: $ 49.82万
• 依托单位: COLUMBIA UNIVERSITY HEALTH SCIENCES
• 依托单位国家: 美国
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-04-01 至 2022-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9898381
• 关键词: 11 cis Retinal; All-Trans-Retinol; Anophthalmos; Binding; Biological Assay; Biological Process; Biophysics; Blindness; Blood Circulation; Calmodulin; Cell membrane; Cells; Cellular Retinol Binding Protein; Complex; Coupled; Cryoelectron Microscopy; Data; Defect; Dependence; Development; Diet; Disease; Enzymes; Equilibrium; Esters; Exhibits; Eye; Fasting; Genes; Genetic Transcription; Health; Human; Hydrophobicity; Intake; Integral Membrane Protein; Knockout Mice; Lead; Length; Ligands; Link; Liver; Mammals; Mediating; Membrane; Metabolism; Microphthalmos; Modeling; Molecular; Molecular Conformation; Molecular Probes; Mutagenesis; Mutation; Names; Nuclear Receptors; Nutrient; Pathology; Pathway interactions; Peptides; Peripheral; Phenotype; Physiological; Positioning Attribute; Proteins; Protomer; Resolution; Retinal Pigments; Retinaldehyde; Retinoids; Retinol Binding Proteins; Roentgen Rays; Role; Route; Signaling Molecule; Site; Structure; System; Techniques; Technology; Testing; Thermodynamics; Time; Tissues; Tretinoin; Vision; Visual system structure; Vitamin A; Vitamins; Woods syndrome; Zebrafish; base; design; design and construction; dimer; disease-causing mutation; experimental study; extracellular; insight; lecithin-retinol acyltransferase; malformation; mutant; new therapeutic target; particle; protein complex; receptor; retinol binding protein receptor; structured data; uptake; visual cycle

Vitamin A is an essential nutrient for all mammals. Many biological processes, including and foremost vision, are crucially dependent on its adequate supply for proper function. Alterations of vitamin A metabolism can result in a wide spectrum of ocular defects and lead to blindness. Retinol (vitamin A alcohol) is the predominant circulating vitamin A form in the fasting state. In times of need (i.e. in the absence of dietary vitamin A intake), in order to distribute vitamin A to the target peripheral tissues, retinol is released in the bloodstream from the liver, the main body storage site of the vitamin, bound to retinol-binding protein (RBP). Inside the cells, retinol binds specific intracellular carriers, namely cellular retinol-binding proteins, and it serves as a precursor for the active vitamin A forms: retinaldehyde, critical for vision, and retinoic acid, the ligand for specific nuclear receptors that regulate the transcription of hundreds of target genes. How retinol is released from the retinol-RBP complex and internalized by the cell has been subject of debate for decades. STRA6, the putative plasma membrane receptor for RBP, was identified in 2007. However, its mechanism of action has remained elusive, not least due to the absence of any structural information. Here we present the structure of STRA6 determined to 4.2 Å resolution by single-particle cryo-electron microscopy. STRA6 is a dimer, with each protomer contributing nine transmembrane and a horizontal intramembrane helix that is positioned at the core of the dimer interface. Unexpectedly, the C-terminus of each protomer is tightly bound to calmodulin in a compact, non-canonical arrangement. The structure suggests possible sites for interaction with extracellular and intracellular carriers for retinol, and modes for internalization of retinol. The atomic model of STRA6 provides a template to guide our understanding at a molecular level on how this protein may function, and to further investigate its physiological role.

维生素A是所有哺乳动物的必需营养素。许多生物过程，包括最重要的视觉，都严重依赖于它的充足供应以实现正常功能。维生素A代谢的改变可导致广泛的眼部缺陷并导致失明。 视黄醇（维生素A醇）是空腹状态下主要的循环维生素A形式。在需要的时候（即在缺乏膳食维生素A摄入的情况下），为了将维生素A分配到目标外周组织，视黄醇从肝脏（维生素的主要身体储存部位）释放到血流中，与视黄醇结合蛋白（RBP）结合。在细胞内，视黄醇结合特定的细胞内载体，即细胞视黄醇结合蛋白，并且它作为活性维生素A形式的前体：对视力至关重要的视黄醇和视黄酸，调节数百个靶基因转录的特定核受体的配体。视黄醇是如何从视黄醇-RBP复合物中释放出来并被细胞内化的，几十年来一直是争论的主题。STRA 6是RBP的假定质膜受体，于2007年被鉴定。然而，其作用机制仍然难以捉摸，尤其是由于缺乏任何结构信息。 在这里，我们提出了结构的STRA 6确定为4.2 μ m的分辨率通过单粒子冷冻电子显微镜。STRA 6是二聚体，每个原聚体贡献九个跨膜和一个位于二聚体界面核心的水平膜内螺旋。出乎意料的是，每个原聚体的C-末端以紧凑的非规范排列与钙调蛋白紧密结合。该结构表明可能的网站与细胞外和细胞内的载体视黄醇的相互作用，和模式的视黄醇的内化。STRA 6的原子模型提供了一个模板，以指导我们在分子水平上了解这种蛋白质的功能，并进一步研究其生理作用。