The protein import channel in the outer mitosomal membrane of Giardia intestinalis

Mol Biol Evol. 2009 Sep;26(9):1941-7. doi: 10.1093/molbev/msp117. Epub 2009 Jun 16.


The identification of mitosomes in Giardia generated significant debate on the evolutionary origin of these organelles, whether they were highly reduced mitochondria or the product of a unique endosymbiotic event in an amitochondrial organism. As the protein import pathway is a defining characteristic of mitochondria, we sought to discover a TOM (translocase in the outer mitochondrial membrane) complex in Giardia. A Hidden Markov model search of the Giardia genome identified a Tom40 homologous sequence (GiTom40), where Tom40 is the protein translocation channel of the TOM complex. The GiTom40 protein is located in the membrane of mitosomes in a approximately 200-kDa TOM complex. As Tom40 was derived in the development of mitochondria to serve as the protein import channel in the outer membrane, its presence in Giardia evidences the mitochondrial ancestry of mitosomes.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Evolution, Molecular
  • Giardia lamblia / metabolism*
  • Immunoprecipitation
  • Mitochondria / metabolism*
  • Mitochondrial Membranes / metabolism*
  • Mitochondrial Proteins / chemistry
  • Mitochondrial Proteins / metabolism*
  • Molecular Sequence Data
  • Protein Structure, Quaternary
  • Protein Transport
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / metabolism*
  • Sequence Alignment


  • Mitochondrial Proteins
  • Protozoan Proteins