The function of a conserved cysteine pair in SRP54

描述（由申请人提供）：信号识别颗粒（SRP）是一种进化上保守的核糖核蛋白，将新生分泌蛋白和膜蛋白靶向内质网。SRP在许多临床相关蛋白的分泌中起作用，并且理解其结构和功能机制对于理解真核细胞中共翻译分泌途径的生物学具有根本重要性。SRP的一种蛋白质，称为SRP 54，整合了颗粒的两个关键活性-识别N-末端信号肽，以及在膜上与SRP受体（SR）形成靶向复合物的GTP依赖性。SRP 54的原核同源物的信号识别和GTdR结构域的晶体结构允许构建真核蛋白的三维模型。在此基础上，在真核生物SRP 54中普遍保守的一对半胱氨酸残基可以被映射到GTdR活性位点口袋的相对侧。这两个残基的功能作用完全未知。我们推测，这两个半胱氨酸，可能是由其他因素，如细胞的氧化还原状态，调节或改变的GTP酶循环的SRP。因此，作为这项工作的第一步，我们的目标是表征SRP 54的GTdR结构域相对于氧化还原和二硫键状态的行为。随后的工作是针对了解半胱氨酸在体内的作用，长期目标是了解其功能的结构基础并确定其生物学意义。虽然该项目的风险较高，但它有可能揭示SRP的一个意想不到的和重要的新监管机制。

DESCRIPTION (provided by applicant): The signal recognition particle (SRP) is an evolutionarily conserved ribonucleoprotein that targets 'nascent secreted and membrane proteins to the endoplasmic reticulum. The SRP plays a role in the secretion of numerous clinically relevant proteins, and an understanding of its structural and functional mechanisms is of fundamental importance for understanding the biology of the co-translational secretion pathway in the the eukaryotic cell. One protein of the SRP, termed SRP54, integrates two key activities of the particle - the recognition of the N-terminal signal peptide, and the GTP-dependent formation of a targeting complex with the SRP receptor (SR) at the membrane. Crystal structures of the signal recognition and GTPase domains of the prokaryotic homolog of SRP54 allow the construction of a three-dimensional model of the eukaryotic protein. On this basis a pair of cysteine residues that are universally conserved in the eukaryotic SRP54 can be mapped to opposite sides of the GTPase active site pocket. The functional role of these two residues is completely unknown. We hypothesize that the two cysteines, perhaps regulated by other factors such as the cellular redox state, modulate or alter the GTPase cycle of the SRP. As a first step in this work, therefore, we aim to characterize the behavior of the GTPase domain of SRP54 with respect to redox and disulfide states. Subsequent work is directed towards understanding the role of the cysteines in vivo, with a long term goal of understanding the structural basis for their function and determining their biological significance. Although the project is somewhat high risk, it has the potential to reveal an unanticipated and significant new regulatory mechanism of the SRP.