Co-evolution of two GTPases enables efficient protein targeting in an RNA-less chloroplast signal recognition particle pathway

Sowmya Chandrasekar, Michael J. Sweredoski, Chang Ho Sohn, Sonja Hess, Shu Ou Shan

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The signal recognition particle (SRP) is an essential ribonucleoprotein particle that mediates the co-translational targeting of newly synthesized proteins to cellular membranes. The SRP RNAis a universally conserved component of SRP that mediates key interactions between two GTPases in SRP and its receptor, thus enabling rapid delivery of cargo to the target membrane. Notably, this essential RNA is bypassed in the chloroplast (cp) SRP of green plants. Previously, we showed that the cpSRP and cpSRP receptor GTPases (cpSRP54 and cpFtsY, respectively) interact efficiently by themselves without the SRP RNA. Here, we explore the molecular mechanism by which this is accomplished. Fluorescence analyses showed that, in the absence of SRP RNA, the M-domain of cpSRP54 both accelerates and stabilizes complex assembly between cpSRP54 and cpFtsY. Crosslinking coupled with mass spectrometry and mutational analyses identified a new interaction between complementarily charged residues on the cpFtsY G-domain and the vicinity of the cpSRP54 M-domain. These residues are specifically conserved in plastids, and their evolution coincides with the loss of SRP RNA in green plants. These results provide an example of how proteins replace the functions of RNA during evolution.

Original languageEnglish
Pages (from-to)386-396
Number of pages11
JournalJournal of Biological Chemistry
Volume292
Issue number1
DOIs
Publication statusPublished - 2017 Jan 6

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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