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Requirements for the import of neisserial Omp85 into the outer membrane of human mitochondria

Christine Ott1, Mandy Utech1, Monika Goetz1

  • 1Department of Microbiology, Biocentre, University of Würzburg, 97074 Würzburg, Germany.

Bioscience Reports
|February 2, 2013
PubMed

Insights

Researchers identified signals targeting bacterial beta-barrel proteins to human mitochondria. The C-terminal region of PorB and specific amino acids in Omp85

Area of Science:

  • Mitochondrial biology
  • Protein import
  • Gram-negative bacteria outer membrane proteins

Background:

  • Beta-barrel proteins reside in outer membranes of Gram-negative bacteria, chloroplasts, and mitochondria.
  • Human mitochondria selectively import bacterial beta-barrel proteins, unlike fungal mitochondria.
  • Enterobacterial proteins are not imported, while some Neisserial proteins are, with Omp85 being the sole integrated example.

Purpose of the Study:

  • To pinpoint the specific signal responsible for targeting Neisserial beta-barrel proteins to human mitochondria.
  • To investigate the roles of different protein domains and sequences in mitochondrial import and integration.

Main Methods:

  • Protein engineering: Exchanging segments between Neisserial Omp85/PorB and E. coli BamA/OmpC.
  • Functional analysis of chimeric proteins to assess mitochondrial targeting and integration.

Main Results:

  • The C-terminal quarter of PorB successfully directed OmpC to mitochondria.
  • Key amino acids within the C-terminal beta-sorting signal of Omp85 were identified as crucial for mitochondrial targeting.
  • Omp85 requires at least two POTRA (polypeptide-transport associated) domains, not just the beta-sorting signal, for membrane integration and function.

Conclusions:

  • The mitochondrial targeting signal for Neisserial beta-barrel proteins is not conserved between PorB and Omp85.
  • A simple linear mitochondrial targeting signal is unlikely.
  • Protein secondary structure may influence the mitochondrial targeting of beta-barrel proteins.

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