A converged ubiquitin-proteasome pathway for the degradation of TOC and TOM tail-anchored receptors

J Integr Plant Biol. 2024 May;66(5):1007-1023. doi: 10.1111/jipb.13645. Epub 2024 Mar 19.

Abstract

In plants, thousands of nucleus-encoded proteins translated in the cytosol are sorted to chloroplasts and mitochondria by binding to specific receptors of the TOC (translocon on the outer chloroplast membrane) and the TOM (translocon on the outer mitochondrial membrane) complexes for import into those organelles. The degradation pathways for these receptors are unclear. Here, we discovered a converged ubiquitin-proteasome pathway for the degradation of Arabidopsis thaliana TOC and TOM tail-anchored receptors. The receptors are ubiquitinated by E3 ligase(s) and pulled from the outer membranes by the AAA+ adenosine triphosphatase CDC48, after which a previously uncharacterized cytosolic protein, transmembrane domain (TMD)-binding protein for tail-anchored outer membrane proteins (TTOP), binds to the exposed TMDs at the C termini of the receptors and CDC48, and delivers these complexes to the 26S proteasome.

Keywords: 26S proteasome; CDC48; SP1; TOC; TOM; ubiquitination.

MeSH terms

  • Arabidopsis Proteins* / metabolism
  • Arabidopsis* / metabolism
  • Proteasome Endopeptidase Complex* / metabolism
  • Proteolysis
  • Ubiquitin* / metabolism
  • Valosin Containing Protein / metabolism

Substances

  • Proteasome Endopeptidase Complex
  • Arabidopsis Proteins
  • Ubiquitin
  • Valosin Containing Protein
  • ATP dependent 26S protease