IRBP: Structure and Function

描述（由申请人提供）：光感受器间视黄酮结合蛋白（IRBP）由光感受器分泌到光感受器间基质中，是视网膜变性的候选物。在基质中，IRBP可以进入Muller细胞绒毛、外段和顶端RPE。Mata等人提出IRBP在Muller细胞和锥体外段之间携带11-顺式和全反式视黄醇。然而，由于对IRBP的结构知之甚少，人们对其作用或其他功能知之甚少。我们的长期目标是确定IRBP的结构和功能之间的关系。IRBP由同源“模块”组成（四足动物中有4个，硬骨鱼中有2个）。每个模块的长度约为300个残基，并结合1到2个类视黄酸或脂肪酸分子。单个模块的x射线晶体结构表现为：1)疏水的- - - - - - -螺旋折叠，2)含有高度保守碱性残基的溶剂暴露表面域。我们的假设是：β - α折叠形成类维甲酸结合位点，表面结构域允许IRBP与基质和/或外段相互作用。这将通过以下补充具体目标进行评估。

DESCRIPTION (provided by applicant): Interphotoreceptor retinoid-binding protein (IRBP), which is secreted by photoreceptors into the interphotoreceptor matrix, is a candidate for retinal degenerations. In the matrix, IRBP has access to Muller cell villi, outer segments, and apical RPE. Mata et al. proposed that IRBP carries 11-cis and all-trans retinol between the Muller cells and cone outer segments. However, this role, or another function is poorly understood because little is known about the structure of IRBP. Our long term goal is to define the relationship between the structure and function of IRBP. IRBP consists of homologous "modules" (4 in tetrapods and 2 in teleost fish). Each module is about 300 residues in length, and binds 1 to 2 molecules of retinoid or fatty acid. The X-ray crystal structure of an individual module shows: 1) a hydrophobic betabetaalpha-spiral fold, and 2) a solvent exposed surface domain containing highly conserved basic residues. Our Hypothesis is: the betabetaalpha fold forms the retinoid-binding site, and the surface domain allows IRBP to interact with the matrix and or outer segment. This will be evaluated through the following complementary Specific Aims. Aim #1: To determine if the betabetaalpha-spiral fold is IRBP's hydrophobic ligand-binding domain, and whether it can discriminate between 11-cis and all-trans retinol. Aim #2: To determine whether the conserved surface domain: 1) binds glycosaminoglycans particularly hyaluronan, and/or 2) facilitates the release or delivery of retinoids at the outer segment. Aim #3: To determine the X-ray crystal structure of the IRBP-ligand complex, and the full-length native bovine IRBP and zebrafish IRBP.