Redox-regulation of enzyme activities involved in methylation cycle and methylation processes

Synthesis and utilisation of methyl groups in plant cells is a cyclic process. The cycle provides S-adenosylmethionine (SAM), which is an intermediate in the biosynthesis of polyamines and of the phytohormone ethylene. However, the majority of SAM (90%) serves as methyl group donor mostly for trans-methylation of DNA. The trans-methylation reactions release S-adenosylhomocysteine (SAH). Since most methyltransferases bind SAH with a higher affinity than SAM, SAH is a potent inhibitor of most SAM-dependent trans-methylations. Therefore, a fast removal of SAH, catalyzed by SAH hydrolase (SAHH), is required for efficient methyltransferase reactions. We identified SAHH and S-adenosylmethionine synthetase 1 (SAMS1) as target for S-nitrosylation and demonstrated that the activity of SAHH and SAMS1 is inhibited by nitric oxide.

We are analysing the physiological function of the NO-dependent inhibition of these two key proteins of the methylation cycle in plants on the biochemical, epigenetic and physiological level.

Eva-Esther Rudolf, Christian Lindermayr

Plant methylation cycle. The cycle provides S-adenosylmethionine, which serves as methyl group donor for transmethylation of DNA and histones. The enzymes highlighted in red have been identified as target for nitric oxide suggesting that this redox molecule is involved in regulation of transmethylation reactions.