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

劳氏眼脑肾综合征（OCRL）是一种酶，其作用是从磷酸肌醇的肌醇环的D-5位去除磷酸。有七种磷酸肌醇，它们是指定亚细胞膜身份的脂质，对调节包括囊泡运输在内的过程至关重要。OCRL的突变与X连锁疾病Lowe综合征有关。这种疾病的特征是肾小管功能障碍、行为困难、发育迟缓和先天性白内障，估计在一般人群中的患病率约为50万分之一。该酶具有四个结构域，从N-末端普列克底物蛋白同源（PH）结构域开始，中心5-磷酸酶结构域作用于PI（4，5）P2和PI（3，4，5）P3，以及C-末端ASPM-SPD 2-hydin（ASH）结构域，其通过疏水界面连接到催化失活的Rho GT3激活（RhoGAP）结构域。OCRL对膜运输过程至关重要，并定位于内吞途径的多个站点。有证据表明，OCRL对PI（4，5）P2的活性甚至在高尔基体、内体和溶酶体上都是关键的，所有这些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OCRL内的各种突变，首先将涉及表征OCRL突变体中的内吞作用过程，主要使用液相染料摄取。该项目的这一方面将涉及利用Dictyosteelium discoideum，它拥有一个单一的OCRL样蛋白，称为Dd 5 P4，参与调节吞噬作用。Dd 5 P4的缺失也不是致命的，使得网骨藻非常便于这项研究。该项目的第二个方面将涉及研究和理解通过使用位于RhoGAP结构域上的称为F&H基序的11-13个氨基酸的小肽基序与OCRL相互作用的三种蛋白质的作用。这三种蛋白质是APPL 1和Ses 1/2内吞衔接蛋白和一种称为Frabin的Rho-鸟嘌呤核苷酸交换因子（GEF）。以前的工作已经证明，ASH-RhoGAP结构域内的错义突变消除了与APPL 1和Ses 1/2蛋白的相互作用，例如，它们各自含有F&H基序。这个项目将提供一个更好的理解机制的见解，为什么OCRL内的这些突变导致劳氏综合征的发病。这项工作也可以长期导致药物的开发来治疗这种疾病，以减轻症状，改善生活质量或延长Lowe综合征患者的寿命超过目前的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.