The goal of this, now amended, first renewal remains to understand Signal Recognition Particle (SRP) dependent targeting of membrane and secretory proteins to the translocation machinery of the cell, at the level of molecular structure and chemical mechanism. This process is highly conserved from bacteria throughout all kingdoms. We have determined structures of the key conserved SRP 54 kD protein (Ffh) of SRP from a thermophilic species, T. aquaticus, including the signal sequence and SRP RNA binding M domain. We determined the structures of 'N' and GTPase domains of Ffh in the apo state which has a key role in the targeting cycle, and the product-like complexes with GDP and Mg++-GDP bound. We have similarly determined the structure of the SRP receptor (SR), FtsY from T. aquaticus, in its apo and its Mg++ GMPPNP bound species. To understand the mechanisms of how these molecules interact as to direct targeting we recently crystallized, and obtained a 1.9A structure of the complex formed between Ffh and FtsY in the presence of a non-hydrolysable GTP analog. This structure beautifully showed how the complex leads to activation of both the GTPases by """"""""substrate twinning"""""""" in which each GTP 3'OH forms a hydrogen bond to the gamma-PO4 of the other GTP. The absence of 3'OH on either of the ribose rings reduces total GTPase activity by approximately 400 fold confirming its role. Thus hydrolysis of GTP would release this linkage and dissociate the complex, as required in the SRP mediated cycle. Mutagenesis suggested by the structure provides support for roles of side chains in the active site. These include an aspartate that is key to activation within each GTPase. We seek to elucidate how binding of signal sequences to SRP, assisted by SRP RNA, is transmitted to the interface formed between SRP and SR. We also seek to harness mutagenesis and structure of the T. aquaticus proteins to define contributions to the specificity of the SRP-SR interface. We also seek to understand the only known case in biology in which the SRP does not contain RNA, in chloroplasts (cp), where a protein cpSRP43 fulfills the role of the RNA, aiming first for crystal structures of the cpSRP-cpSRP43-cpSR complex. These will instruct in the mechanism of replacing the role of RNA by protein, and therefore in the essence of the dynamic roles of SRP RNA and cpSRP43.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM060641-08
Application #
7255805
Study Section
Biophysical Chemistry Study Section (BBCB)
Program Officer
Shapiro, Bert I
Project Start
2000-01-01
Project End
2009-06-30
Budget Start
2007-07-01
Budget End
2009-06-30
Support Year
8
Fiscal Year
2007
Total Cost
$312,701
Indirect Cost
Name
University of California San Francisco
Department
Biochemistry
Type
Schools of Medicine
DUNS #
094878337
City
San Francisco
State
CA
Country
United States
Zip Code
94143
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Korennykh, Alexei V; Egea, Pascal F; Korostelev, Andrei A et al. (2009) The unfolded protein response signals through high-order assembly of Ire1. Nature 457:687-93
Egea, Pascal F; Napetschnig, Johanna; Walter, Peter et al. (2008) Structures of SRP54 and SRP19, the two proteins that organize the ribonucleic core of the signal recognition particle from Pyrococcus furiosus. PLoS One 3:e3528
Egea, Pascal F; Tsuruta, Hiro; de Leon, Gladys P et al. (2008) Structures of the signal recognition particle receptor from the archaeon Pyrococcus furiosus: implications for the targeting step at the membrane. PLoS One 3:e3619
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Egea, Pascal F; Stroud, Robert M; Walter, Peter (2005) Targeting proteins to membranes: structure of the signal recognition particle. Curr Opin Struct Biol 15:213-20
Chu, Feixia; Shan, Shu-ou; Moustakas, Demetri T et al. (2004) Unraveling the interface of signal recognition particle and its receptor by using chemical cross-linking and tandem mass spectrometry. Proc Natl Acad Sci U S A 101:16454-9