Localization and nucleotide specificity of Blastocystis succinyl-CoA synthetase

Mol Microbiol. 2008 Jun;68(6):1395-405. doi: 10.1111/j.1365-2958.2008.06228.x. Epub 2008 Apr 29.


The anaerobic lifestyle of the intestinal parasite Blastocystis raises questions about the biochemistry and function of its mitochondria-like organelles. We have characterized the Blastocystis succinyl-CoA synthetase (SCS), a tricarboxylic acid cycle enzyme that conserves energy by substrate-level phosphorylation. We show that SCS localizes to the enigmatic Blastocystis organelles, indicating that these organelles might play a similar role in energy metabolism as classic mitochondria. Although analysis of residues inside the nucleotide-binding site suggests that Blastocystis SCS is GTP-specific, we demonstrate that it is ATP-specific. Homology modelling, followed by flexible docking and molecular dynamics simulations, indicates that while both ATP and GTP fit into the Blastocystis SCS active site, GTP is destabilized by electrostatic dipole interactions with Lys 42 and Lys 110, the side-chains of which lie outside the nucleotide-binding cavity. It has been proposed that residues in direct contact with the substrate determine nucleotide specificity in SCS. However, our results indicate that, in Blastocystis, an electrostatic gatekeeper controls which ligands can enter the binding site.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Blastocystis / chemistry
  • Blastocystis / cytology*
  • Blastocystis / enzymology*
  • Blastocystis / genetics
  • Blastocystis Infections / parasitology
  • Cytoplasmic Structures / chemistry
  • Cytoplasmic Structures / enzymology
  • Cytoplasmic Structures / genetics
  • Humans
  • Kinetics
  • Models, Molecular
  • Molecular Sequence Data
  • Phylogeny
  • Protein Subunits / chemistry
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism
  • Purine Nucleotides / metabolism*
  • Sequence Alignment
  • Substrate Specificity
  • Succinate-CoA Ligases / chemistry*
  • Succinate-CoA Ligases / genetics
  • Succinate-CoA Ligases / metabolism
  • Swine / genetics


  • Protein Subunits
  • Protozoan Proteins
  • Purine Nucleotides
  • Succinate-CoA Ligases

Associated data

  • GENBANK/EU076378
  • GENBANK/EU076379
  • GENBANK/EU076380
  • GENBANK/EU090061