Related Experiment Video
Updated: Jun 21, 2026

Protein-protein Interactions Visualized by Bimolecular Fluorescence Complementation in Tobacco Protoplasts and Leaves
Published on: March 9, 2014
A distinct mechanism to achieve efficient signal recognition particle (SRP)-SRP receptor interaction by the
Peera Jaru-Ampornpan1, Thang X Nguyen, Shu-Ou Shan
1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
Abstract:
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.
Related Concept Videos
Cell Signaling in Plants
Protein Transport to the Thylakoids
Directing Proteins to the Rough Endoplasmic Reticulum
Protein Transport to the Outer Chloroplast Membrane
Two models describe the mechanism of precursor recognition and entry across the outer membrane through the TOC complex. Model 1 suggests the newly synthesized precursor binds to the TOC receptor 159 and forms a complex.
Protein Transport to the Inner Chloroplast Membrane
Photoreceptors and Plant Responses to Light

