Outer membrane proteins derived from non-cyanobacterial lineage cover the peptidoglycan of cyanophora paradoxa cyanelles and serve as a cyanelle diffusion channel

Seiji Kojima, Koji Muramoto, Tomonobu Kusano

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

The cyanelle is a primitive chloroplast that contains a peptidoglycan layer between its inner and outer membranes. Despite the fact that the envelope structure of the cyanelle is reminiscent of Gram-negative bacteria, the Cyanophora paradoxa genome appears to lack genes encoding homologs of putative peptidoglycan-associated outer membrane proteins and outer membrane channels. These are key components of Gram-negative bacterial membranes, maintaining structural stability and regulating permeability of outer membrane, respectively. Here, we discovered and characterized two dominant peptidoglycan-associated outer membrane proteins of the cyanelle (∼2 × 106 molecules per cyanelle). We named these proteins CppF and CppS (cyanelle peptidoglycan-associated proteins). They are homologous to each other and function as a diffusion channel that allows the permeation of compounds with Mr <1,000 as revealed by permeability measurements using proteoliposomes reconstituted with purified CppS and CppF. Unexpectedly, amino acid sequence analysis revealed no evolutionary linkage to cyanobacteria, showing only a moderate similarity to cell surface proteins of bacteria belonging to Planctomycetes phylum. Our findings suggest that the C. paradoxa cyanelle adopted non-cyanobacterial lineage proteins as its main outer membrane components, providing a physical link with the underlying peptidoglycan layer and functioning as a diffusion route for various small substances across the outer membrane.

Original languageEnglish
Pages (from-to)20198-20209
Number of pages12
JournalJournal of Biological Chemistry
Volume291
Issue number38
DOIs
Publication statusPublished - 2016 Sep 16

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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