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Co-translational capturing of nascent ribosomal proteins by their dedicated chaperones.

Pausch P, Singh U, Ahmed YL, Pillet B, Murat G, Altegoer F, Stier G, Thoms M, Hurt E, Sinning I, Bange G, Kressler D - Nat Commun (2015)

Bottom Line: Owing to their difficult physicochemical properties, the synthesis of assembly-competent ribosomal proteins represents a major challenge.Recent evidence highlights that dedicated chaperone proteins recognize the N-terminal regions of ribosomal proteins and promote their soluble expression and delivery to the assembly site.Co-translational capturing of nascent ribosomal proteins by dedicated chaperones constitutes an elegant mechanism to prevent unspecific interactions and aggregation of ribosomal proteins on their road to incorporation.

View Article: PubMed Central - PubMed

Affiliation: LOEWE Center for Synthetic Microbiology (SYNMIKRO) and Department of Chemistry, Philipps-University Marburg, Hans-Meerwein-Straße, Marburg D-35043, Germany.

ABSTRACT
Exponentially growing yeast cells produce every minute >160,000 ribosomal proteins. Owing to their difficult physicochemical properties, the synthesis of assembly-competent ribosomal proteins represents a major challenge. Recent evidence highlights that dedicated chaperone proteins recognize the N-terminal regions of ribosomal proteins and promote their soluble expression and delivery to the assembly site. Here we explore the intuitive possibility that ribosomal proteins are captured by dedicated chaperones in a co-translational manner. Affinity purification of four chaperones (Rrb1, Syo1, Sqt1 and Yar1) selectively enriched the mRNAs encoding their specific ribosomal protein clients (Rpl3, Rpl5, Rpl10 and Rps3). X-ray crystallography reveals how the N-terminal, rRNA-binding residues of Rpl10 are shielded by Sqt1's WD-repeat β-propeller, providing mechanistic insight into the incorporation of Rpl10 into pre-60S subunits. Co-translational capturing of nascent ribosomal proteins by dedicated chaperones constitutes an elegant mechanism to prevent unspecific interactions and aggregation of ribosomal proteins on their road to incorporation.

No MeSH data available.


Related in: MedlinePlus

Model highlighting the co-translational capturing of selected ribosomal proteins by their dedicated chaperones.Simplified model for the stable incorporation of Rpl10 into cytoplasmic pre-60S subunits (upper left part). The chaperone Sqt1 recognizes the N-terminal residues of Rpl10 as these emerge from translating ribosomes and the Sqt1–Rpl10 complex is released into the cytoplasm upon translation termination. We propose that initial docking of Sqt1-bound Rpl10 onto Lsg1-defined pre-60S subunits involves Rpl10 surfaces that are not shielded by Sqt1 and likely occurs at pre-60S sites that are not masked by Nmd3 (see Discussion section). Subsequently, the activity of the GTPase Lsg1 entails structural rearrangements that promote the release of Nmd3 and the stable incorporation of Rpl10, thus leading to the generation of mature 60S subunits that can engage in translation initiation. General model for the co-translational capturing of ribosomal proteins by their specific chaperone partners (lower left part). This study has revealed that the chaperones Rrb1, Syo1 and Yar1 are also recruited to their distinct ribosomal protein clients (Rpl3, Rpl5 and Rps3), as these are synthesized from their mRNAs by the ribosome. While the Rrb1-Rpl3 and Syo1-Rpl5-Rpl11 complexes are imported into the nucleus where these ribosomal proteins assemble into pre-60S subunits, it is not yet clear whether Yar1 travels together with Rps3 into the nucleus or promotes pre-40S assembly of Rps3 in the cytoplasm. After extensive nuclear maturation (right part), pre-60S particles gain export competence upon recruitment of Nmd3, which is recognized by the exportin Crm1, and travel across the nuclear pore complex to the cytoplasm.
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f8: Model highlighting the co-translational capturing of selected ribosomal proteins by their dedicated chaperones.Simplified model for the stable incorporation of Rpl10 into cytoplasmic pre-60S subunits (upper left part). The chaperone Sqt1 recognizes the N-terminal residues of Rpl10 as these emerge from translating ribosomes and the Sqt1–Rpl10 complex is released into the cytoplasm upon translation termination. We propose that initial docking of Sqt1-bound Rpl10 onto Lsg1-defined pre-60S subunits involves Rpl10 surfaces that are not shielded by Sqt1 and likely occurs at pre-60S sites that are not masked by Nmd3 (see Discussion section). Subsequently, the activity of the GTPase Lsg1 entails structural rearrangements that promote the release of Nmd3 and the stable incorporation of Rpl10, thus leading to the generation of mature 60S subunits that can engage in translation initiation. General model for the co-translational capturing of ribosomal proteins by their specific chaperone partners (lower left part). This study has revealed that the chaperones Rrb1, Syo1 and Yar1 are also recruited to their distinct ribosomal protein clients (Rpl3, Rpl5 and Rps3), as these are synthesized from their mRNAs by the ribosome. While the Rrb1-Rpl3 and Syo1-Rpl5-Rpl11 complexes are imported into the nucleus where these ribosomal proteins assemble into pre-60S subunits, it is not yet clear whether Yar1 travels together with Rps3 into the nucleus or promotes pre-40S assembly of Rps3 in the cytoplasm. After extensive nuclear maturation (right part), pre-60S particles gain export competence upon recruitment of Nmd3, which is recognized by the exportin Crm1, and travel across the nuclear pore complex to the cytoplasm.

Mentions: Elegant work from the Johnson laboratory has revealed that Sqt1, Rpl10 and the GTPase Lsg1 are required for the release of the export adaptor Nmd3 from cytoplasmic pre-60S subunits, and that, moreover, Sqt1 is only significantly associated with Nmd3- and Lsg1-containing pre-60S subunits upon overexpression of dominant-negative Lsg1(K349T) mutant protein3843. Accordingly, it has been proposed that Lsg1 promotes and couples Nmd3 release to Rpl10 docking on a transient pre-60S intermediate containing Lsg1, Nmd3 and the Sqt1-bound Rpl10 (ref. 38). The structural insight provided by this study, in combination with the 60S crystal structure and the recent identification of the rRNA-binding sites of Nmd3 (refs 1, 49), allows proposing a refined model for the above-mentioned pre-60S maturation events. Since the main rRNA-binding sites of Nmd3 (H38, H69 and H89; ref. 49) and Rpl10 (H38 and H89; ref. 1) are partially overlapping, Nmd3 and Rpl10 cannot bind simultaneously with their maximal affinities to pre-60S subunits. Therefore, Rpl10, whose access to H89 is blocked due to Sqt1 being bound to its N-terminal residues, must initially be recruited via interaction sites that are not masked by Nmd3. Potential candidate sites that could mediate initial Rpl10 binding consist of the base of H38 and the last α-helix within the eukaryote-specific C-terminal extension of Rpl5 (ref. 1). While the base of H38 makes extensive contacts with different regions along Rpl10, the α-helix of Rpl5 interacts with the C-terminal α-helix of the eukaryote-specific extension of Rpl10 (amino acids 169–221; Supplementary Fig. 1). However, it remains to be determined whether or how the initial docking or stable incorporation of Rpl10 may contribute to the recently described rotation of the 5S RNP and H38 into their final position50, since the Lsg1-defined cytoplasmic pre-60S subunits may have already adopted this conformation. Upon initial binding of Rpl10, the GTPase Lsg1, either due to GTP binding or GTP hydrolysis, may then promote structural rearrangements that weaken the association of Nmd3, thereby allowing recognition of H89 by Rpl10, and thus facilitating the transfer of the N-terminal Rpl10 residues from Sqt1 into H89. Finally, these interconnected events would have entailed structural alterations that are only compatible with complete docking of Rpl10 and release of Nmd3 (for a simplified model, see Fig. 8).


Co-translational capturing of nascent ribosomal proteins by their dedicated chaperones.

Pausch P, Singh U, Ahmed YL, Pillet B, Murat G, Altegoer F, Stier G, Thoms M, Hurt E, Sinning I, Bange G, Kressler D - Nat Commun (2015)

Model highlighting the co-translational capturing of selected ribosomal proteins by their dedicated chaperones.Simplified model for the stable incorporation of Rpl10 into cytoplasmic pre-60S subunits (upper left part). The chaperone Sqt1 recognizes the N-terminal residues of Rpl10 as these emerge from translating ribosomes and the Sqt1–Rpl10 complex is released into the cytoplasm upon translation termination. We propose that initial docking of Sqt1-bound Rpl10 onto Lsg1-defined pre-60S subunits involves Rpl10 surfaces that are not shielded by Sqt1 and likely occurs at pre-60S sites that are not masked by Nmd3 (see Discussion section). Subsequently, the activity of the GTPase Lsg1 entails structural rearrangements that promote the release of Nmd3 and the stable incorporation of Rpl10, thus leading to the generation of mature 60S subunits that can engage in translation initiation. General model for the co-translational capturing of ribosomal proteins by their specific chaperone partners (lower left part). This study has revealed that the chaperones Rrb1, Syo1 and Yar1 are also recruited to their distinct ribosomal protein clients (Rpl3, Rpl5 and Rps3), as these are synthesized from their mRNAs by the ribosome. While the Rrb1-Rpl3 and Syo1-Rpl5-Rpl11 complexes are imported into the nucleus where these ribosomal proteins assemble into pre-60S subunits, it is not yet clear whether Yar1 travels together with Rps3 into the nucleus or promotes pre-40S assembly of Rps3 in the cytoplasm. After extensive nuclear maturation (right part), pre-60S particles gain export competence upon recruitment of Nmd3, which is recognized by the exportin Crm1, and travel across the nuclear pore complex to the cytoplasm.
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Related In: Results  -  Collection

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Show All Figures
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f8: Model highlighting the co-translational capturing of selected ribosomal proteins by their dedicated chaperones.Simplified model for the stable incorporation of Rpl10 into cytoplasmic pre-60S subunits (upper left part). The chaperone Sqt1 recognizes the N-terminal residues of Rpl10 as these emerge from translating ribosomes and the Sqt1–Rpl10 complex is released into the cytoplasm upon translation termination. We propose that initial docking of Sqt1-bound Rpl10 onto Lsg1-defined pre-60S subunits involves Rpl10 surfaces that are not shielded by Sqt1 and likely occurs at pre-60S sites that are not masked by Nmd3 (see Discussion section). Subsequently, the activity of the GTPase Lsg1 entails structural rearrangements that promote the release of Nmd3 and the stable incorporation of Rpl10, thus leading to the generation of mature 60S subunits that can engage in translation initiation. General model for the co-translational capturing of ribosomal proteins by their specific chaperone partners (lower left part). This study has revealed that the chaperones Rrb1, Syo1 and Yar1 are also recruited to their distinct ribosomal protein clients (Rpl3, Rpl5 and Rps3), as these are synthesized from their mRNAs by the ribosome. While the Rrb1-Rpl3 and Syo1-Rpl5-Rpl11 complexes are imported into the nucleus where these ribosomal proteins assemble into pre-60S subunits, it is not yet clear whether Yar1 travels together with Rps3 into the nucleus or promotes pre-40S assembly of Rps3 in the cytoplasm. After extensive nuclear maturation (right part), pre-60S particles gain export competence upon recruitment of Nmd3, which is recognized by the exportin Crm1, and travel across the nuclear pore complex to the cytoplasm.
Mentions: Elegant work from the Johnson laboratory has revealed that Sqt1, Rpl10 and the GTPase Lsg1 are required for the release of the export adaptor Nmd3 from cytoplasmic pre-60S subunits, and that, moreover, Sqt1 is only significantly associated with Nmd3- and Lsg1-containing pre-60S subunits upon overexpression of dominant-negative Lsg1(K349T) mutant protein3843. Accordingly, it has been proposed that Lsg1 promotes and couples Nmd3 release to Rpl10 docking on a transient pre-60S intermediate containing Lsg1, Nmd3 and the Sqt1-bound Rpl10 (ref. 38). The structural insight provided by this study, in combination with the 60S crystal structure and the recent identification of the rRNA-binding sites of Nmd3 (refs 1, 49), allows proposing a refined model for the above-mentioned pre-60S maturation events. Since the main rRNA-binding sites of Nmd3 (H38, H69 and H89; ref. 49) and Rpl10 (H38 and H89; ref. 1) are partially overlapping, Nmd3 and Rpl10 cannot bind simultaneously with their maximal affinities to pre-60S subunits. Therefore, Rpl10, whose access to H89 is blocked due to Sqt1 being bound to its N-terminal residues, must initially be recruited via interaction sites that are not masked by Nmd3. Potential candidate sites that could mediate initial Rpl10 binding consist of the base of H38 and the last α-helix within the eukaryote-specific C-terminal extension of Rpl5 (ref. 1). While the base of H38 makes extensive contacts with different regions along Rpl10, the α-helix of Rpl5 interacts with the C-terminal α-helix of the eukaryote-specific extension of Rpl10 (amino acids 169–221; Supplementary Fig. 1). However, it remains to be determined whether or how the initial docking or stable incorporation of Rpl10 may contribute to the recently described rotation of the 5S RNP and H38 into their final position50, since the Lsg1-defined cytoplasmic pre-60S subunits may have already adopted this conformation. Upon initial binding of Rpl10, the GTPase Lsg1, either due to GTP binding or GTP hydrolysis, may then promote structural rearrangements that weaken the association of Nmd3, thereby allowing recognition of H89 by Rpl10, and thus facilitating the transfer of the N-terminal Rpl10 residues from Sqt1 into H89. Finally, these interconnected events would have entailed structural alterations that are only compatible with complete docking of Rpl10 and release of Nmd3 (for a simplified model, see Fig. 8).

Bottom Line: Owing to their difficult physicochemical properties, the synthesis of assembly-competent ribosomal proteins represents a major challenge.Recent evidence highlights that dedicated chaperone proteins recognize the N-terminal regions of ribosomal proteins and promote their soluble expression and delivery to the assembly site.Co-translational capturing of nascent ribosomal proteins by dedicated chaperones constitutes an elegant mechanism to prevent unspecific interactions and aggregation of ribosomal proteins on their road to incorporation.

View Article: PubMed Central - PubMed

Affiliation: LOEWE Center for Synthetic Microbiology (SYNMIKRO) and Department of Chemistry, Philipps-University Marburg, Hans-Meerwein-Straße, Marburg D-35043, Germany.

ABSTRACT
Exponentially growing yeast cells produce every minute >160,000 ribosomal proteins. Owing to their difficult physicochemical properties, the synthesis of assembly-competent ribosomal proteins represents a major challenge. Recent evidence highlights that dedicated chaperone proteins recognize the N-terminal regions of ribosomal proteins and promote their soluble expression and delivery to the assembly site. Here we explore the intuitive possibility that ribosomal proteins are captured by dedicated chaperones in a co-translational manner. Affinity purification of four chaperones (Rrb1, Syo1, Sqt1 and Yar1) selectively enriched the mRNAs encoding their specific ribosomal protein clients (Rpl3, Rpl5, Rpl10 and Rps3). X-ray crystallography reveals how the N-terminal, rRNA-binding residues of Rpl10 are shielded by Sqt1's WD-repeat β-propeller, providing mechanistic insight into the incorporation of Rpl10 into pre-60S subunits. Co-translational capturing of nascent ribosomal proteins by dedicated chaperones constitutes an elegant mechanism to prevent unspecific interactions and aggregation of ribosomal proteins on their road to incorporation.

No MeSH data available.


Related in: MedlinePlus