How do rare endosomal pools of phosphoinositide lipids lead to the congenital disorder Oculocerebral renal syndrome of Lowe (Lowe Syndrome)?

ococococerebrorenal Syndrome of Lowe （ocl）是一种酶，其作用是从磷酸肌醇环的D-5位置去除磷酸盐。有七种磷酸肌苷，它们是指定亚细胞膜身份的脂质，对包括囊泡运输在内的调节过程至关重要。ocl的突变与x连锁疾病Lowe综合征有关。这种疾病的特点是肾小管功能障碍、行为困难、发育迟缓和先天性白内障，在一般人群中估计患病率约为50万分之一。该酶具有四个结构域，从n端Pleckstrin Homology （PH）结构域开始，一个作用于PI(4,5)P2和PI(3,4,5)P3的中心5-磷酸酶结构域和一个c端ASPM-SPD2-hydin （ASH）结构域，该结构域通过疏水界面连接到催化无活性的Rho GTPase激活（RhoGAP）结构域。ocl对膜运输过程至关重要，定位于内吞途径的多个站点。有证据表明，ocl对PI(4,5)P2的活性甚至对高尔基体、核内体和溶酶体至关重要，它们都具有非常低水平的PI(4,5)P2。该项目将涉及研究与Lowe综合征相关的ocl中的各种突变，首先将涉及表征ocl突变体的内吞作用过程，主要使用液相染料摄取。该项目的这一方面将涉及利用盘状盘基骨菌，它拥有一种称为Dd5P4的ocl样蛋白，参与吞噬作用的调节。Dd5P4的缺失也不是致命的，这使得盘基ostelium非常便于本研究。该项目的第二个方面将涉及通过使用位于RhoGAP结构域的11-13个氨基酸的小肽基序F&H基序来研究和理解与ocl相互作用的三种蛋白质的作用。所讨论的三种蛋白质是APPL1和Ses1/2内吞衔接蛋白和称为Frabin的罗鸟嘌呤核苷酸交换因子（GEF）。先前的研究表明，ASH-RhoGAP结构域内的错义突变会破坏与APPL1和Ses1/2蛋白的相互作用，这两个蛋白都含有一个F&H基序。该项目将总体上更好地理解为什么ocl中的这些突变会导致Lowe综合征的发病。从长远来看，这项工作也可能导致治疗这种疾病的药物的开发，以减轻症状，改善生活质量，或延长患有洛氏综合征的人的寿命，超过目前的40岁。

Oculocerebrorenal Syndrome of Lowe (OCRL) is an enzyme, which acts to remove a phosphate from the D-5 position of the inositol ring of phosphoinositides. There are seven phosphoinositides, which are lipids that specify subcellular membrane identity and are crucial for regulating processes including vesicular trafficking. Mutations in OCRL have been associated with the X-linked disorder, Lowe syndrome. This disease is characterised by renal tubular dysfunction, behavioural difficulties, developmental delay and congenital cataracts and has an estimated prevalence of approximately 1 in 500,000 in the general population. This enzyme possesses four domains, starting with the N-terminal Pleckstrin Homology (PH) domain, a central 5-phosphatase domain that acts against PI(4,5)P2 and PI(3,4,5)P3 and a C-terminal ASPM-SPD2-hydin (ASH) domain linked by a hydrophobic interface to a catalytically inactive Rho GTPase activating (RhoGAP) domain. OCRL is critical for the process of membrane trafficking and localises to multiple stations of the endocytic pathway. Evidence has arisen that the activity of OCRL against PI(4,5)P2 is even critical on the Golgi, endosomes and lysosomes, all of which possess very low levels of PI(4,5)P2. This project will involve studying various mutations within OCRL linked to Lowe syndrome and firstly will involve characterising the process of endocytosis in OCRL mutants, mainly using fluid-phase dye uptake. This aspect of the project will involve utilising Dictyostelium discoideum, which possesses a single OCRL-like protein, known as Dd5P4, which is involved in the regulation of phagocytosis. The loss of Dd5P4 is also not lethal, making Dictyostelium highly convenient for this study. The second aspect of this project would involve studying and understanding the role of the three proteins that interact with OCRL through usage of a small 11-13 amino acid peptide motif called the F&H motif, located on the RhoGAP domain. The three proteins in question are the APPL1 and Ses1/2 endocytic adaptor proteins and a Rho-guanine nucleotide exchange factor (GEF) called Frabin. Previous work has demonstrated that missense mutations within the ASH-RhoGAP domain abolish interactions with APPL1 and Ses1/2 proteins for example, which each contain an F&H motif. This project will overall provide a greater understanding of the mechanistic insights as to why these mutations within OCRL lead to the onset of Lowe syndrome. This work could also in the long-term lead to the development of drugs to treat this disease to alleviate the symptoms and improve the quality of life or extend the life span of individuals with Lowe syndrome beyond the current 40 years of age.