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）：眼镜是一种独特的结构，精心设计，可将光线集中在视网膜上，该过程需要根据眼睛与它所重点关注的对象的距离进行实质性变化。要完成其功能，镜头也必须是透明的，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，这些膜在维持晶状体稳态和透明度方面起着至关重要的作用。高度专业的膜通道和转运蛋白是微循环系统的基础，该系统为较深的纤维细胞提供营养，并清除废物。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降低到小于光的波长的距离，这是避免透镜组织散布光的重要先决条件。该建议的重点是在透镜纤维细胞中发现的两种主要膜蛋白，即四叠蛋白MP20和水准蛋白MIP（也称为Aquaporin-0）。这两种膜蛋白中的任何一个突变都会导致白内障的形成，表明它们对适当的晶状体功能的重要性。 关于MP20以及其他四叠腺苷的结构信息仍然很少。因此，特定目标1是为了确定MP20的结构，主要是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。对于MP20获得的结构信息将有助于建模四叠腺苷家族的其他成员的结构，这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。特定的目标2用于通过进一步研究其与Galectin-3的相互作用（一种突出的粘附调节剂）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是否可以与透镜特异性整联蛋白结合，因为已知许多四翼烷蛋白与整合素相互作用，尤其是如果这些蛋白质包含B1亚基。 MIP作为水和小无负荷分子的孔的功能得到了很好的特征，但是与其他水通道蛋白MIP不同，MIP也具有粘合特性，并且可以形成细胞间交界，可能会在纤维细胞之间产生连续的水孔。特定目标3的目的是使用X射线和电子晶体学的组合为MIP介导的膜连接创建伪原子模型。膜连接的结构将揭示水孔相互作用在相互作用的MIP四聚体中的排列，这对透镜中的微循环系统的功能具有重要意义。