Crosstalk between Mitochondrial Malate Dehydrogenase and Cytochrome bc1 Complex

Abstract

The cytochrome bc1 complex (bc1) catalyzes electron transfer from ubiquinol to cytochrome c with concomitantly translocating protons across the membrane to generate a proton gradient and membrane potential for driving ATP synthesis. Recently we found that mitochondrial soluble matrix proteins could increase the activity of bc1 complex. To identify the protein(s) that is responsible for the activity enhancement, the purified, detergent dispersed bc1 complex was incubated with soluble mitochondrial matrix proteins followed by an extensive dialysis in the absence of detergent to pull down the interacting protein(s) with bc1 complex upon centrifugation. SDS-PAGE analysis of the precipitate showed that several proteins from matrix were in the precipitates in addition to the subunits of bc1 complex. One of the matrix proteins with molecular weight of 35.6 kD was identified to be mitochondria malate dehydrogenase (MDH) by MALDI-TOF Mass spectrometry. The identification of MDH was further confirmed by western blot with anti-MDH antibody. Incubating purified MDH with detergent dispersed bc1 complex increases activities of bc1 compelx and MDH. The effect of bc1 complex on the activities of MDH is unidirectional (oxalacetate ––> malate). This novel crosstalk between citric acid cycle enzymes and electron transfer chain complexes might play a regulatory role in mitochondrial bioenergetics. This work was supported in part by a grant from NIH (GM30721).