MLQ protein regulates association of mitochondrially encoded subunits Fo-a and A6L with ATP synthase complex

The biogenesis of mammalian ATP synthase is complex process believed to proceed via several modules. The final phase is represented by incorporation of the two mtDNA-encoded subunits Fo-a and A6L, and probably of the two newly described accessory subunits DAPIT and MLQ. To confirm this, we followed the assembly state of ATP synthase in rho0 cells lacking both subunits Fo-a and A6L, cells harbouring 9205delTA microdeletion lacking subunit Fo-a, HEK293 cells with knockdown of DAPIT and HEK293 cells with knockout of MLQ. Absence of either Fo-a alone or Fo-a and A6L or MLQ results into the normal levels of labile, ~50 kDa smaller complex, which lacks all four subunits (Fo-a, A6L, DAPIT and MLQ). In all the cell lines tested we found that the total amount of individual subunits corresponds well with the amount of the subunit, associated with fully assembled ATP synthase complex. In the cells lacking MLQ the biosynthesis and assembly of both subunits Fo-a and A6L is preserved, but these subunits are fast degraded. We conclude that MLQ, Fo-a and A6L closely associate and their presence within the complex depends on each another. On the contrary, DAPIT protein seems to be incorporated at the very last step.