The glutathione redox milieu of the IMS is controlled by the cytosol

The glutathione redox milieu of the IMS is controlled by the cytosol.

Kerstin Kojer, Heike Gangel, Jan Riemer

Proteins of the intermembrane space (IMS) of mitochondria are important for the assembly of the respiratory chain, the detoxification of reactive oxygen species and the initiation of apoptotic processes. These events are highly regulated and often depend on the local redox environment that is mainly controlled by the local glutathione redox buffer. To characterize the dynamics of this glutathione redox buffer, we used redox sensors (Grx1-roGFP2) that we specifically targeted to the cytosol, the IMS and the matrix. Our dynamic analyses were based on measurements of the recovery of the glutathione redox state after oxidative shock. In wild type cells the redox buffer is reducing in these compartments and recovers rapidly after oxidation. The deletion of the central reducing enzyme of the glutathione redox system, glutathione reductase (Glr1) resulted in a striking delay of this recovery. Since Glr1 is a dually localized enzyme found in the cytosol and the matrix we next complemented the GLR1 deletion strain with cytosolic Glr1. This resulted in a recovery of the redox buffer in the cytosol and the IMS but not in the matrix. To further detail this finding we relied on a ZWF1 deletion strain. Zwf1 provides the cytosol with reduced NADPH, the electron donor for Glr1. We observed an inhibition of the recovery of the glutathione buffer in the cytosol and the IMS but not in the matrix emphasizing that glutathione can freely diffuse between the cytosol and the IMS.