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Localization and nucleotide specificity of Blastocystis succinyl‐CoA synthetase
Author(s) -
Hamblin Karleigh,
Standley Daron M.,
Rogers Matthew B.,
Stechmann Alexandra,
Roger Andrew J.,
Maytum Robin,
Van Der Giezen Mark
Publication year - 2008
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2008.06228.x
Subject(s) - biology , blastocystis , gtp' , nucleotide , biochemistry , organelle , binding site , enzyme , mitochondrion , microbiology and biotechnology , gene , feces
Summary 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.