Demonstration of a multistep mechanism for assembly of the SRP x SRP receptor complex: implications for the catalytic role of SRP RNA |
| |
Authors: | Zhang Xin Kung Simon Shan Shu-ou |
| |
Institution: | Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA |
| |
Abstract: | Two GTPases in the signal recognition particle (SRP) and its receptor (SR) control the delivery of newly synthesized proteins to the endoplasmic reticulum or plasma membrane. During the protein targeting reaction, the 4.5S SRP RNA accelerates the association between the two GTPases by 400-fold. Using fluorescence resonance energy transfer, we demonstrate here that formation of a stable SRP·SR complex involves two distinct steps: a fast initial association between SRP and SR to form a GTP-independent early complex and then a GTP-dependent conformational rearrangement to form the stable final complex. We also found that the 4.5S SRP RNA significantly stabilizes the early GTP-independent intermediate. Furthermore, mutational analyses show that there is a strong correlation between the ability of the mutant SRP RNAs to stabilize the early intermediate and their ability to accelerate SRP·SR complex formation. We propose that the SRP RNA, by stabilizing the early intermediate, can give this transient intermediate a longer life time and therefore a higher probability to rearrange to the stable final complex. This provides a coherent model that explains how the 4.5S RNA exerts its catalytic role in SRP·SR complex assembly. |
| |
Keywords: | SRP signal recognition particle SR signal recognition particle receptor ER endoplasmic reticulum FRET fluorescence resonance energy transfer RNC ribosome· nascent chain complex DACM maleimide-coumarin BODIPY-FL maleimide-BODIPY-fluorescein GppNHp 5&prime -guanylylimido-diphosphate pPL preprolactin |
本文献已被 ScienceDirect PubMed 等数据库收录! |