Structure and Function of Lens Membrane Proteins

晶状体膜蛋白的结构和功能

• 批准号: 7171776
• 负责人: THOMAS WALZ
• 金额: $ 32.92万
• 依托单位: HARVARD MEDICAL SCHOOL
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-01-01 至 2008-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7171776
• 关键词: Address; Adhesions; Adhesives; Apoptosis; Architecture; Area; Binding; Cataract; Cell Adhesion; Cell Adhesion Molecules; Cell physiology; Cells; Complex; Condition; Crystalline Lens; Crystallization; Depth; Electron Microscopy; Electrons; Eye; Family; Family member; Galactose Binding Lectin; Galectin 3; Homeostasis; Insecta; Integral Membrane Protein; Integrins; Intercellular Junctions; Ion Channel; Lead; Lens Fiber; Light; MIP gene; Mediating; Membrane; Membrane Proteins; Microcirculation; Microscopic; Modeling; Molecular; Mutation; Nutrient; Pathway interactions; Personal Satisfaction; Play; Polysaccharides; Principal Investigator; Process; Property; Protein Overexpression; Proteins; Reporting; Research; Resolution; Retina; Roentgen Rays; Role; Shapes; Structure; System; Techniques; Testing; Tissues; Transmembrane Domain; Tubular formation; Virus-like particle; Waste Products; Water; Work; X ray diffraction analysis; X-Ray Crystallography; base; design; electron crystallography; fiber cell; human PHEMX protein; image processing; image reconstruction; indexing; interest; lens; light scattering; member; migration; novel; particle; programs; reconstitution; research study; solute; two-dimensional; water channel

DESCRIPTION (provided by applicant): The ocular lens is a unique structure exquisitely designed to focus light onto the retina, a process that requires substantial shape changes of the lens according to the distance of the eye from the object it is focusing on. To accomplish its function, the lens also has to be transparent, and it has to provide a high index of refraction. We are interested in the structure and function of membrane proteins in the lens, which play crucial roles in maintaining lens homeostasis and transparency. A highly specialized array of membrane channels and transporters is the basis for a microcirculation system that supplies deeper-lying fiber cells with nutrients and clears them of waste products. Moreover, membrane proteins mediate the tight packing of the fiber cells, thus reducing spaces between cells to a distance smaller than the wavelength of light, an important prerequisite to avoid light scattering by the lens tissue. This proposal focuses on the two major membrane proteins found in lens fiber cells, the tetraspanin MP20 and the aquaglyceroporin MIP (also referred to as aquaporin-0). Mutations in either one of these two membrane proteins lead to the formation of cataracts, demonstrating their importance for proper lens function. Structural information on MP20 as well as other tetraspanins is still sparse. Specific Aim 1 is thus to determine the structure of MP20 primarily by electron microscopy but also pursuing an X-ray crystallographic approach. The structural information obtained for MP20 will be useful to model the structure of other members of the tetraspanin family, which are important in many cellular processes, such as cell adhesion, proliferation, activation, migration, and apoptosis. Specific Aim 2 is directed towards characterizing the function of MP20 as a cell adhesion molecule by further studies of its interaction with galectin-3, a prominent adhesion modulator. We will also determine whether MP20 can bind to lens-specific integrins, as many tetraspanins are known to interact with integrins, especially if these contain a b1 subunit. The function of MIP as a pore for water and small uncharged molecules is well characterized, but unlike other aquaporins MIP also has adhesive properties and can form intercellular junctions, possibly creating continuous water pores between fiber cells. The objective of Specific Aim 3 is to create a pseudo-atomic model for the MIP-mediated membrane junction using a combination of X-ray and electron crystallography. The structure of the membrane junction will reveal the arrangement of the water pores in interacting MIP tetramers, which has important implications for the functioning of the microcirculation system in the lens.

描述（由申请人提供）：目镜是一种独特的结构，经过精心设计，可将光线聚焦到视网膜上，这一过程需要根据眼睛与其聚焦物体的距离来改变晶状体的形状。为了实现其功能，透镜还必须是透明的，并且必须提供高折射率。我们对晶状体中膜蛋白的结构和功能感兴趣，它们在维持晶状体稳态和透明度方面发挥着至关重要的作用。高度专业化的膜通道和转运蛋白阵列是微循环系统的基础，该系统为深层纤维细胞提供营养并清除其中的废物。此外，膜蛋白介导纤维细胞的紧密堆积，从而将细胞之间的空间减少到小于光波长的距离，这是避免晶状体组织光散射的重要先决条件。该提案重点关注晶状体纤维细胞中发现的两种主要膜蛋白，即四跨膜蛋白 MP20 和水甘油孔蛋白 MIP（也称为水通道蛋白-0）。这两种膜蛋白中任何一种的突变都会导致白内障的形成，这表明它们对于晶状体正常功能的重要性。 关于 MP20 以及其他四跨膜蛋白的结构信息仍然很少。因此，具体目标 1 是主要通过电子显微镜确定 MP20 的结构，但也采用 X 射线晶体学方法。 MP20 获得的结构信息将有助于模拟四跨膜蛋白家族其他成员的结构，这些成员在许多细胞过程中很重要，例如细胞粘附、增殖、激活、迁移和凋亡。具体目标 2 旨在通过进一步研究 MP20 与 galectin-3（一种重要的粘附调节剂）的相互作用来表征 MP20 作为细胞粘附分子的功能。我们还将确定 MP20 是否可以与晶状体特异性整合素结合，因为已知许多四跨膜蛋白与整合素相互作用，特别是如果它们含有 b1 亚基。 MIP 作为水和不带电小分子的孔的功能已得到充分表征，但与其他水通道蛋白不同的是，MIP 还具有粘合特性，可以形成细胞间连接，可能在纤维细胞之间形成连续的水孔。具体目标 3 的目标是结合使用 X 射线和电子晶体学，为 MIP 介导的膜连接创建伪原子模型。膜连接的结构将揭示相互作用的 MIP 四聚体中水孔的排列，这对晶状体中微循环系统的功能具有重要意义。