S-Adenosylmethionine Synthetase Is Essential for Parasite Survival through a Complex Interaction Network with Cytoplasmic and Nuclear Proteins.

S-adenosylmethionine synthetase (SAMS) is a key enzyme for the synthesis of the lone methyl donor S-adenosyl methionine (SAM), which is involved in transmethylation reactions and hence required for cellular processes such as DNA, RNA, and histone methylation, but also polyamine biosynthesis and proteostasis. In the human malaria parasite , SAMS is encoded by a single gene and has been suggested to be crucial for malaria pathogenesis and transmission; however, to date, SAMS has not been fully characterized. To gain deeper insight into the function of SAMS, we generated a conditional gene knockdown (KD) using the ribozyme system. We show that SAMS localizes to the cytoplasm and the nucleus of blood-stage parasites. SAMS-KD results in reduced histone methylation and leads to impaired intraerythrocytic growth and gametocyte development. To further determine the interaction network of SAMS, we performed a proximity-dependent biotin identification analysis. We identified a complex network of 1114 proteins involved in biological processes such as cell cycle control and DNA replication, or transcription, but also in phosphatidylcholine and polyamine biosynthesis and proteasome regulation. Our findings highlight the diverse roles of SAMS during intraerythrocytic growth and sexual stage development and emphasize that SAMS is a potential drug target.