Efficient Interaction between Two GTPases Allows the Chloroplast SRP Pathway to Bypass the Requirement for an SRP RNA

Jaru-Ampornpan, Peera; Chandrasekar, Sowmya; Shan, Shu‐ou

doi:10.1091/mbc.e07-01-0037

Cited by 42 publications

(82 citation statements)

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“…Instead, the cpSRP consists of the cpSRP54 GTPase and a novel protein only found in chloroplast, cpSRP43 (Schuenemann et al, 1998). Previously, we showed that cpSRP54 and cpFtsY can form a complex with one another at rates 200-fold faster than that of their bacterial homologues, thereby bypassing the requirement for the SRP RNA (Jaru-Ampornpan et al, 2007). Here, we underscored the molecular mechanisms underlying the large difference in interaction rates between the bacterial and chloroplast SRP and SR GTPases.…”

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confidence: 65%

“…Previously, we showed that cpSRP54 and cpFtsY can form a complex with one another at rates 200-fold faster than that of their bacterial homologues, thereby bypassing the requirement for the SRP RNA (Jaru-Ampornpan et al, 2007). Here, we underscored the molecular mechanisms underlying the large difference in interaction rates between the bacterial and chloroplast SRP and SR GTPases.Previous biochemical and structural works have suggested a model in which the conformational rearrangement at the N-G-domain interface required for SRP • SR complex formation is partly achieved in free cpFtsY, thus allowing it to interact more efficiently with its binding partner cpSRP54 (Jaru-Ampornpan et al, 2007;Chandrasekar et al, 2008). In this work, we provide independent biochemical support for this model by showing that cpFtsY is 5-to 10-fold more efficient at interacting with the GTPase domain of SRP, even when the binding partner is the heterologous E. coli Ffh (Figure 1).…”

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confidence: 66%

“…Previous kinetic analyses revealed that in the absence of the SRP RNA, the association kinetics between cpSRP54 and cpFtsY is 200-fold faster than that of their Escherichia coli homologues and matches the rate of the RNA-stimulated interaction between bacterial SRP and SR (Jaru-Ampornpan et al, 2007). This provides a simple explanation for the absence of the SRP RNA in the cpSRP pathway, but also raises additional questions.…”

Section: Introductionmentioning

confidence: 96%

“…Instead, a novel 43-kDa protein, cpSRP43, binds to a unique C-terminal extension in cpSRP54, and together the cpSRP43 • cpSRP54 complex constitutes the chloroplast SRP (Groves et al, 2001). Although early models suggested that cpSRP43 might act as a functional homologue of the SRP RNA to regulate the GTPase activity of the chloroplast SRP and SRP receptor (see below; Goforth et al, 2004), kinetic analyses showed that cpSRP43 does not considerably affect either the complex formation or GTP hydrolysis rates of cpSRP54 and cpFtsY (Jaru-Ampornpan et al, 2007). Instead, cpSRP43 interacts specifically with the cargo, the LHCPs, to facilitate substrate recognition (Delille et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

“…For the E. coli GTPases, k cat /K m is equal to the association rate constant between SRP and SR during complex formation (Peluso et al, 2001). For the chloroplast GTPases, this rate constant provides a lower limit for the association rate constant between cpSRP54 and cpFtsY to form an active complex (Jaru-Ampornpan et al, 2007). In situations where the values of k cat are comparable, the differences in k cat /K m reflect differences in either the rate or stability of complex formation.…”

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confidence: 99%

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A Distinct Mechanism to Achieve Efficient Signal Recognition Particle (SRP)–SRP Receptor Interaction by the Chloroplast SRP Pathway

Jaru-Ampornpan

Nguyen

Shan

2009

MBoC

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Cotranslational protein targeting by the signal recognition particle (SRP) requires the SRP RNA, which accelerates the interaction between the SRP and SRP receptor 200-fold. This otherwise universally conserved SRP RNA is missing in the chloroplast SRP (cpSRP) pathway. Instead, the cpSRP and cpSRP receptor (cpFtsY) by themselves can interact 200-fold faster than their bacterial homologues. Here, cross-complementation analyses revealed the molecular origin underlying their efficient interaction. We found that cpFtsY is 5-to 10-fold more efficient than Escherichia coli FtsY at interacting with the GTPase domain of SRP from both chloroplast and bacteria, suggesting that cpFtsY is preorganized into a conformation more conducive to complex formation. Furthermore, the cargo-binding M-domain of cpSRP provides an additional 100-fold acceleration for the interaction between the chloroplast GTPases, functionally mimicking the effect of the SRP RNA in the cotranslational targeting pathway. The stimulatory effect of the SRP RNA or the M-domain of cpSRP is specific to the homologous SRP receptor in each pathway. These results strongly suggest that the M-domain of SRP actively communicates with the SRP and SR GTPases and that the cytosolic and chloroplast SRP pathways have evolved distinct molecular mechanisms (RNA vs. protein) to mediate this communication. INTRODUCTIONThe signal recognition particle (SRP) and the SRP receptor (SR) comprise the major cellular machineries that cotranslationally deliver newly synthesized proteins from the cytosol to target membranes (Walter and Johnson, 1994;Keenan et al., 2001). Cotranslational protein targeting begins with recognition of the cargo-ribosomes translating nascent polypeptides containing signal sequences-by the SRP (Walter et al., 1981). The cargo is brought to the vicinity of the target membrane via the interaction between the SRP and SRP receptor (FtsY in bacteria) (Gilmore et al., 1982a). On arrival at the membrane, SRP unloads its cargo to the protein-conducting channel, composed of the sec61p complex in eukaryotic cells or secYEG complex in bacteria and archaea (Simon and Blobel, 1991;Gorlich et al., 1992;Halic et al., 2006). The SRP and SRP receptor also reciprocally stimulate each other's GTPase activity (Powers and Walter, 1995). Thus, after cargo unloading, guanosine triphosphate (GTP) hydrolysis drives disassembly of the SRP • SR complex, returning the components into the cytosol for the next round of protein targeting (Connolly et al., 1991).The SRP pathway is conserved throughout all three kingdoms of life. Although the protein components of SRP and SR vary across species, the functional core of SRP is a highly conserved ribonucleoprotein complex, composed of a 54-kDa SRP GTPase (SRP54 in eukaryotes or Ffh in bacteria) and an SRP RNA (Keenan et al., 2001). The SRP receptor also contains a conserved GTPase domain that is highly homologous to the GTPase domain in SRP54, and together the GTPase domains of SRP and SR form a unique subgroup in the GTPase superfamily (Keen...

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confidence: 65%

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confidence: 66%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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A Distinct Mechanism to Achieve Efficient Signal Recognition Particle (SRP)–SRP Receptor Interaction by the Chloroplast SRP Pathway

Jaru-Ampornpan

Nguyen

Shan

2009

MBoC

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An ankyrin repeat chaperone targets toxic oligomers during amyloidogenesis

Gupta,

Lu,

Wang

et al. 2023

Protein Science

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Numerous age‐linked diseases are rooted in protein misfolding; this has motivated the development of small molecules and therapeutic antibodies that target the aggregation of disease‐linked proteins. Here we explore another approach: molecular chaperones with engineerable protein scaffolds such as the ankyrin repeat domain (ARD). We tested the ability of http://firstglance.jmol.org/fg.htm?mol=3DEO, a small, robust, ATP‐ and cofactor‐independent plant chaperone built from an ARD, to antagonize disease‐linked protein aggregation. http://firstglance.jmol.org/fg.htm?mol=3DEO delays the aggregation of multiple proteins including the amyloid beta peptide (Aβ) associated with Alzheimer's disease and α‐synuclein associated with Parkinson's disease. Kinetic modeling and biochemical analyses show that http://firstglance.jmol.org/fg.htm?mol=3DEO targets early oligomers during Aβ aggregation, preventing their transition to a self‐propagating nucleus on the fibril surface. Accordingly, http://firstglance.jmol.org/fg.htm?mol=3DEO rescued neuronal cells from the toxicity of extracellular Aβ42 aggregates. The substrate‐binding domain of http://firstglance.jmol.org/fg.htm?mol=3DEO, composed primarily of the ARD, is necessary and sufficient to prevent Aβ42 aggregation and protect cells against Aβ42 toxicity. This work provides an example in which an ARD chaperone non‐native to mammalian cells harbors anti‐amyloidal activity, which may be exploited for bioengineering.

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RNase P from Organelles

Vioque

2009

Ribonuclease P

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Efficient Interaction between Two GTPases Allows the Chloroplast SRP Pathway to Bypass the Requirement for an SRP RNA

Cited by 42 publications

References 50 publications

A Distinct Mechanism to Achieve Efficient Signal Recognition Particle (SRP)–SRP Receptor Interaction by the Chloroplast SRP Pathway

A Distinct Mechanism to Achieve Efficient Signal Recognition Particle (SRP)–SRP Receptor Interaction by the Chloroplast SRP Pathway

An ankyrin repeat chaperone targets toxic oligomers during amyloidogenesis

RNase P from Organelles

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