Structure and Function of Lens Membrane Proteins

晶状体膜蛋白的结构和功能

• 批准号: 7342072
• 负责人: THOMAS WALZ
• 金额: $ 27.24万
• 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 2009-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7342072
• 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）：晶状体是一种独特的结构，设计精美，用于将光线聚焦到视网膜上，这一过程需要晶状体根据眼睛与其聚焦物体的距离发生实质性的形状变化。为了实现它的功能，镜片还必须是透明的，并且它必须提供高折射率。我们对晶状体中膜蛋白的结构和功能感兴趣，它们在维持晶状体的稳态和透明度方面起着至关重要的作用。高度专业化的膜通道和转运体阵列是微循环系统的基础，为深层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，从而将细胞之间的距离缩小到小于光的波长，这是避免光被晶状体组织散射的重要先决条件。本研究的重点是在晶状体纤维细胞中发现的两种主要膜蛋白，四跨蛋白MP20和水甘油三酯oporin MIP（也称为水通道蛋白0）。这两种膜蛋白中的任何一种的突变都会导致白内障的形成，这证明了它们对晶状体正常功能的重要性。