Protein-lysine methyltransferase that selectively trimethylates citrate synthase (CS) in mitochondria (PubMed:28391595, PubMed:28887308). Seems to conduct trimethylation in a highly distributive manner rather than in a processive manner, and thus introduces a single methyl group per binding event (PubMed:28887308). . This is the function of CSKMT (citrate synthase lysine methyltransferase, ENSG00000214756).