Mitochondrial protein-lysine N-methyltransferase that trimethylates adenine nucleotide translocases ANT2/SLC25A5 and ANT3/SLC25A6, thereby regulating mitochondrial respiration. Probably also trimethylates ANT1/SLC25A4. L-lysyl-[protein] + 3 S-adenosyl-L-methionine = 3 H(+) + N(6),N(6),N(6)-trimethyl-L-lysyl-[protein] + 3 S-adenosyl-L-homocysteine The pre-methyltransferase (preMT) region is responsible for mitochondrial localization. Belongs to the ANT/ATPSC lysine N-methyltransferase family.