TbLOK1/ATOM19 is a novel subunit of the noncanonical mitochondrial outer membrane protein translocase of Trypanosoma brucei

Mol Microbiol. 2016 Nov;102(3):520-529. doi: 10.1111/mmi.13476. Epub 2016 Aug 18.


TbLOK1 has previously been characterized as a trypanosomatid-specific mitochondrial outer membrane protein whose ablation caused a collapse of the mitochondrial network, disruption of the membrane potential and loss of mitochondrial DNA. Here we show that ablation of TbLOK1 primarily abolishes mitochondrial protein import, both in vivo and in vitro. Co-immunprecipitations together with blue native gel analysis demonstrate that TbLOK1 is a stable and stoichiometric component of the archaic protein translocase of the outer membrane (ATOM), the highly diverged functional analogue of the TOM complex in other organisms. Furthermore, we show that TbLOK1 together with the other ATOM subunits forms a complex functional network where ablation of individual subunits either causes degradation of a specific set of other subunits or their exclusion from the ATOM complex. In summary these results establish that TbLOK1 is an essential novel subunit of the ATOM complex and thus that its primary molecular function is linked to mitochondrial protein import across the outer membrane. The previously described phenotypes can all be explained as consequences of the lack of mitochondrial protein import. We therefore suggest that in line with the nomenclature of the ATOM complex subunits, TbLOK1 should be renamed to ATOM19.

MeSH terms

  • Carrier Proteins / metabolism*
  • Membrane Proteins / metabolism*
  • Membrane Transport Proteins / metabolism*
  • Mitochondria / metabolism
  • Mitochondrial Membranes / metabolism
  • Mitochondrial Precursor Protein Import Complex Proteins
  • Mitochondrial Proteins / metabolism
  • Protein Subunits
  • Protein Transport / physiology
  • Protozoan Proteins / metabolism
  • Trypanosoma brucei brucei / genetics
  • Trypanosoma brucei brucei / metabolism*


  • Carrier Proteins
  • Membrane Proteins
  • Membrane Transport Proteins
  • Mitochondrial Precursor Protein Import Complex Proteins
  • Mitochondrial Proteins
  • Protein Subunits
  • Protozoan Proteins