Interdependence of cardiolipin biosynthesis and mitochondrial respiratory chain function

My PhD dissertation work has focused on studying the function and regulation of cardiolipin (CL) with respect to the mitochondrial respiratory chain in the yeast S. cerevisiae. CL is a phospholipid, typically present in membranes containing respiratory chain complexes, such as the mitochondrial inner membrane. In order to determine the role of CL in respiratory chain supercomplex (complex III + complex IV) formation, I initiated a collaborative project with Prof. Hermann Schagger (University of Frankfurt) and showed that CL is required for the stability of supercomplexes (Pfeiffer et al. , 2003). Based on the previous studies on CL regulation and CL synthase properties, I hypothesized that CL biosynthesis can be regulated by the mitochondrial matrix pH. By carrying out in vivo pulse labeling experiments on the yeast respiratory chain complex assembly mutants and by using specific respiratory chain inhibitors, I showed that my hypothesis was correct (Gohil et al., 2004). These findings suggest that CL stabilizes respiratory chain supercomplexes, which in turn regulate CL biosynthesis by regulating CL synthase activity via mitochondrial matrix pH.; In a project to identify proteins that interact with CL synthase, I used an epitope tagged CL synthase and showed that it is functional and enriched in the mitochondria. Two dimensional separation of mitochondrial membrane proteins isolated from mitochondria containing epitope tagged CL synthase showed that CL is associated with respiratory complex III (in collaboration with Prof. Hermann Schagger). Physical interaction of CL synthase with complex III shows that CL is directly delivered to one of the components of the supercomplex, complex III. Taken together, my work provides a molecular mechanism underlying the interdependence of mitochondrial membrane proteins and phospholipids involved in the biogenesis of mitochondrial membrane.; My last project was focused on elucidating CL function by identifying genes that show a synthetic lethal interaction with CL synthase. To this end, I constructed a crd1Delta strain in the appropriate genetic background and showed a synthetic lethal interaction between mitochondrial CL and phosphatidylethanolamine (PE) biosynthetic machinery. This suggests that PE can substitute for some functions of CL and vice versa. However, the absence of both results in inviability.