Population of ATP synthase molecules in mitochondria is limited by available 6.8-kDa proteolipid protein (MLQ)

A 6.8-kDa proteolipid (called MLQ) is a hydrophobic mitochondrial protein with unknown function that is loosely associated with ATP Synthase. Here, we show that MLQ-knockdown HeLa cells lose population of ATP Synthase in mitochondria. This is not due to low transcription of subunit genes of ATP Synthase because levels of mRNA for α- and β-subunits are unaffected by the knockdown. As a consequence, the knockdown cells show low mitochondrial ATP synthesis activity, grow slowly in the normal medium, and are vulnerable to glucose deprivation. Given that the expression of MLQ varies responding to cellular conditions, MLQ is a potential regulator of the mitochondrial ATP synthesis.