Characterization of COQ4 in the synthesis of coenzyme Q6 in S. cerevisiae

Abstract

Coenzyme Q is a redox lipid that has important functions in the cell such as the transport of electrons from complex I, and II to complex III in the mitochondrial respiratory chain and its role as antioxidant. At least, nine genes (COQ1-COQ9) are involved in the biosynthesis of this molecule, among them COQ4. COQ4 is essential for the synthesis of CoQ in eukaryotes, but until this moment, its exact function remains unknown. Furthermore, this gene has gained more importance in the last years because several cases of patients with CoQ deficiency syndrome associated to mutations in COQ4 have been described (Salviati et al., 2012). In yeast, Coqs proteins form a multienzymatic complex organised around Coq4p (Marbois et al., 2009), which seems to have no enzymatic activity but plays a structural role in the complex. In order to discover the function of Coq4p in the synthesis of CoQ is necessary to study both its interaction with others Coqs proteins and the exact point in the biosynthetic process in which Coq4p takes part. Yeast mutants harbouring deletions in COQ3-COQ9 genes accumulate the same early precursor, hexaprenyl hidroxybenzoate (HHB) (Clarke, 2001). However, it has been reported that a null COQ7 mutant yeast over-expressing ABC1/COQ8 accumulates a CoQ late intermediate, demethoxy-Q6 (DMQ) (Padilla et al., 2008). This model can be very useful to study the action point of Coq4p in the CoQ biosynthetic pathway. In order to elucidate the function of Coq4p, we have developed several point mutants in COQ4 as well as a COQ4/COQ7 double mutant. Based in results obtained from these mutants, we propose that COQ4 is necessary in the earliest stage in the assembly of de CoQ biosynthetic complex.