Abstract Protein biogenesis is essential in all cells and initiates when a nascent polypeptide emerges from the ribosome exit tunnel, where multiple ribosome-associated protein biogenesis factors (RPBs) direct nascent proteins to distinct fates. How distinct RPBs spatiotemporally coordinate with one another to affect accurate protein biogenesis is an emerging question. Here, we address this question by studying the role of a cotranslational chaperone, nascent polypeptide-associated complex (NAC), in regulating substrate selection by signal recognition particle (SRP), a universally conserved protein targeting machine. We show that mammalian SRP and SRP receptors (SR) are insufficient to generate the biologically required specificity for protein targeting to the endoplasmic reticulum. NAC co-binds with and remodels the conformational landscape of SRP on the ribosome to regulate its interaction kinetics with SR, thereby reducing the nonspecific targeting of signalless ribosomes and pre-emptive targeting of ribosomes with short nascent chains. Mathematical modeling demonstrates that the NAC-induced regulations of SRP activity are essential for the fidelity of cotranslational protein targeting. Our work establishes a molecular model for how NAC acts as a triage factor to prevent protein mislocalization, and demonstrates how the macromolecular crowding of RPBs at the ribosome exit site enhances the fidelity of substrate selection into individual protein biogenesis pathways.
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Fidelity of Cotranslational Protein Targeting to the Endoplasmic Reticulum
Fidelity of protein targeting is essential for the proper biogenesis and functioning of organelles. Unlike replication, transcription and translation processes, in which multiple mechanisms to recognize and reject noncognate substrates are established in energetic and molecular detail, the mechanisms by which cells achieve a high fidelity in protein localization remain incompletely understood. Signal recognition particle (SRP), a conserved pathway to mediate the localization of membrane and secretory proteins to the appropriate cellular membrane, provides a paradigm to understand the molecular basis of protein localization in the cell. In this chapter, we review recent progress in deciphering the molecular mechanisms and substrate selection of the mammalian SRP pathway, with an emphasis on the key role of the cotranslational chaperone NAC in preventing protein mistargeting to the ER and in ensuring the organelle specificity of protein localization.
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- Award ID(s):
- 1929452
- NSF-PAR ID:
- 10354898
- Date Published:
- Journal Name:
- International Journal of Molecular Sciences
- Volume:
- 23
- Issue:
- 1
- ISSN:
- 1422-0067
- Page Range / eLocation ID:
- 281
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary Activation of nucleotide‐binding leucine‐rich repeat receptors (NLRs) results in immunity and a localized cell death. NLR cell death activity requires oligomerization and in some cases plasma membrane (PM) localization. The exact mechanisms underlying PM localization of NLRs lacking predicted transmembrane domains or recognizable lipidation motifs remain elusive.
We used confocal microscopy, genetically encoded molecular tools and protein‐lipid overlay assays to determine whether PM localization of members of the Arabidopsis HeLo‐/RPW8‐like domain ‘helper’ NLR (RNL) family is mediated by the interaction with negatively charged phospholipids of the PM.
Our results show that PM localization and stability of some RNLs and one CC‐type NLR (CNL) depend on the direct interaction with PM phospholipids. Depletion of phosphatidylinositol‐4‐phosphate from the PM led to a mis‐localization of the analysed NLRs and consequently inhibited their cell death activity. We further demonstrate homo‐ and hetero‐association of members of the RNL family. Our results provide new insights into the molecular mechanism of NLR localization and defines an important role of phospholipids for CNL and RNL PM localization and consequently, for their function.
We propose that RNLs interact with anionic PM phospholipids and that RNL‐mediated cell death and immune responses happen at the PM.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/ijms23010281
