Mitochondrial Genome Integrity Mutations Uncouple the Yeast Saccharomyces cerevisiae ATP Synthase

Yamin Wang,Usha Singh,David M Mueller

doi:10.1074/jbc.m609635200

Abstract

The mitochondrial ATP synthase is a molecular motor, which couples the flow of protons with phosphorylation of ADP. Rotation of the central stalk within the core of ATP synthase effects conformational changes in the active sites driving the synthesis of ATP. Mitochondrial genome integrity (mgi) mutations have been previously identified in the alpha-, beta-, and gamma-subunits of ATP synthase in yeast Kluyveromyces lactis and trypanosome Trypanosoma brucei. These mutations reverse the lethality of the loss of mitochondrial DNA in petite negative strains. Introduction of the homologous mutations in Saccharomyces cerevisiae results in yeast strains that lose mitochondrial DNA at a high rate and accompanied decreases in the coupling of the ATP synthase. The structure of yeast F1-ATPase reveals that the mgi residues cluster around the gamma-subunit and selectively around the collar region of F1. These results indicate that residues within the mgi complementation group are necessary for efficient coupling of ATP synthase, possibly acting as a support to fix the axis of rotation of the central stalk.

Highlights

The ATP synthase is composed of a membrane-bound F0 portion and a water soluble F1
A family of nuclear mutations, mitochondrial genome integrity, has been identified in K. lactis, which convert it from petite negative to petite positive
To gain a better understanding on the effect of these mutations on the biochemistry of the ATP synthase, we have made a subset of the corresponding mutations in yeast S. cerevisiae and tested the resulting genetic, growth, and biochemical phenotypes

Summary

Mutations Uncoupling the ATP Synthase

The bloodstream form of Trypanosoma brucei normally requires expression of the mitochondrial genome despite the absence of oxidative phosphorylation in this stage of the life cycle. There is a naturally occurring bloodstream form of trypanosome, dyskinetoplastic, that lacks mtDNA This form has been shown to have sequence variation in the gene encoding the ␥-subunit, which allows this bloodstream form of trypanosome to survive without mitochondrial gene expression [14]. Changes in the axis of rotation of the central stalk are predicted to alter the interactions of the ␥-subunit with the core of the F1-ATPase and reduce the coupling of the ATP synthase. These results provide information on the structure/ function relationship for the residues classified as mgi

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION