Crosstalk between cytochrome bc1 complex and mitochondrial matrix enzymes

Scope and Method of Study: ; Protein pull-down assay, western blotting, protein activity assay, superoxide assay, Surface Pasmon Resonance, Mass Spectroscopy, Cross linking. ; Findings and Conclusions: ; The interactions between the mitochondrial cytochrome bc 1 complex and matrix soluble proteins were studied by a precipitation pull-down technique. One of the matrix proteins pulled down by bc 1 complex was identified as mitochondrial malate dehydrogenase (MDH) by MALDI-TOF Mass spectrometry and confirmed by Western blotting with anti-MDH antibody. Using cross linking technique, subunits I, II (core I & II) and V of the bc 1 complex were identified as the interacting sites for MDH. Incubating purified MDH with the detergent dispersed bc 1 complex results in the increase of the activities of both the bc 1 complex and MDH. The effect of the bc 1 complex on the activities of MDH is unidirectional (oxalacetate -> malate). These results suggest that the novel crosstalk between citric acid cycle enzymes and electron transfer chain complexes might play a regulatory role in mitochondrial bioenergetics. We also confirmed the existence of a short form of MDH. We found that it does not have the normal enzyme activity but may help the normal long MDH together to regulate the bioenergetics process. ; Another matrix protein pulled down by bc 1 complex was identified as mitochondrial aconitase. Subunit II of the bc 1 complex was identified as the interacting site for aconitase. Unlike MDH, no effect on the activity of the bc 1 complex was observed when purified aconitase was interacted with the detergent dispersed bc 1 complex. And the activity of aconitase was only enhanced slightly by cytochrome bc 1 complex. Upon the binding of aconitase, the superoxide generating activity of bc 1 complex is greatly decreased. However, when aconitase was added to the bacterial bc 1 complex, little effect on its superoxide generating activity was observed. The lack of core subunits I and II in the bacterial bc 1 complex may be the ...