Kontrollmechanismen von GTPasen der Rho-Familie

Rho家族的小鸟苷三磷酸酶（或gtpase）是多种不同（病理）生化过程中信号转导的关键介质。Rho GTPases调节因子功能的丧失或获得通常被认为是信号强度改变的潜在原因，也很可能是它们功能障碍的原因。在理解Rho GTPases调控的结构-功能关系方面已经取得了很大进展，然而，这些调控因子是如何控制自己的还不清楚。在这个项目的第一个资助期内，我们对dcl1和OPHN1蛋白的分析结果非常吸引人，令人鼓舞。我们将x连锁智力低下蛋白OPHNl的BAR结构域描述为具有双重功能的模块，即膜结合和弯曲功能，以及顺式作用的RhoGAP结构域结合和自抑制功能。与OPHNl相反，我们发现肿瘤抑制蛋白DLC1的RhoGAP功能不是通过顺式抑制（通过SAM或START结构域），而是通过ras特异性p120RasGAP的SH3结构域的反式抑制机制有效关闭的。对这些数据的进一步分析将为破译这些关键的Rho GTPase调节因子的结构功能关系提供一些重要的见解，并将扩大我们对（病理）生化机制的理解。因此，我们的目标是在第二个（第4至第6年）资助期内调查以下要点：(i)通过结构和突变分析完成我们对bar介导的OPNH1自身抑制的分子基础的研究，（ii）对细胞和脂质体中OPHN1野生型和组成型活性突变体的功能监测和成像，（iii）使用纯化的突触体组分鉴定和表征“OPHN1激活因子”（OAF）， （iv）分析结构，调控，调节蛋白14-3-3γ和抑制蛋白p120RasGAP存在时，DLC1蛋白的特异性和功能。计划的研究将通过蛋白质化学，生物化学以及分子，结构和细胞生物学的既定技术来实现。解决这些至关重要的问题将最终推进我们在信号转导领域的知识，并揭示失调信号通路的分子细节。

Small guanosine triphosphatases (or GTPases) of the Rho family are key mediators of signal transduction in a multitude of diverse (patho)biochemical processes. Loss or gain of function of regulators of Rho GTPases is generally accepted as potential cause for an altered signaling strength and highly likely the reason for their dysfunctions. Much progress has been made towards understanding the structure-function relationship in respect to the regulation of Rho GTPases, however, it is still unclear how these regulators are controlled themselves. What emerged out of our analysis of DLC1 and OPHN1 proteins within the first funding period of this project is very engaging and encouraging. We described the BAR domain of the X-linked mental retardation protein OPHNl as a module with dual functions, a membrane binding and bending function, and a cis-acting RhoGAP domain binding and autoinhibiting function. Contrary to OPHNl, we found that the RhoGAP function of the tumor suppressor protein DLC1 is efficiently shut down not via a cis-inhibitory (by SAM or START domains) but via a trans-inhibitory mechanism by the SH3 domain of the Ras-specific p120RasGAP. Further analysis of these data will provide several important insights in deciphering structure function relationships of these critical Rho GTPase regulators and will expand our understanding of (patho)biochemical mechanisms. Thus, we aim at investigating the following points within the second (year 4 to 6) funding period: (i) finalizing our investigations of the molecular basis of the BAR-mediated autoinhibition of OPNH1 by structural and mutational analysis, (ii) functional monitoring and imaging of OPHN1 wild-type and constitutive active mutants in cells and on liposomes, (iii) identification and characterization of an 'OPHN1 activating factor' (OAF) using purified synaptosomal fractions, (iv) analysis of structure, regulation, specificity and function of DLC1 protein in the presence of the modulatory protein 14-3-3γ and inhibitory protein p120RasGAP. Planned studies will be achieved by the established techniques of protein chemistry, biochemistry as well as molecular, structural and cellular biology. Addressing these issues of fundamental importance will ultimately advance our knowledge in the field of signal transduction and disclose molecular details of dysregulated signaling pathways.