TY - JOUR
T1 - Demonstration of a Multistep Mechanism for Assembly of the SRP·SRP Receptor Complex
T2 - Implications for the Catalytic Role of SRP RNA
AU - Zhang, Xin
AU - Kung, Simon
AU - Shan, Shu ou
N1 - Funding Information:
This work was supported by the National Institutes of Health through grant GM078024 to S.S. S.S. was supported by a Burroughs Wellcome Fund Career Award, the Henry and Camille Dreyfus Foundation, a Beckman Young Investigator Award, and a Packard and Lucile Award in Science and Engineering. X.Z. was supported by a fellowship from the Ulric B. and Evelyn L. Bray Endowment Fund. We thank members of the Shan laboratory for their comments on the manuscript.
PY - 2008/9/5
Y1 - 2008/9/5
N2 - 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.
AB - 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.
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U2 - 10.1016/j.jmb.2008.05.049
DO - 10.1016/j.jmb.2008.05.049
M3 - Article
C2 - 18617187
AN - SCOPUS:47849117948
SN - 0022-2836
VL - 381
SP - 581
EP - 593
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 3
ER -