Copper Ions InhibitS-Adenosylhomocysteine Hydrolase by Causing Dissociation of NAD⁺Cofactor

Abstract

S-Adenosylhomocysteine hydrolase (SAHH) regulates biomethylation and homocysteine metabolism and thus is an attractive target in drug design studies. SAHH has been shown to be a copper binding protein in vivo; however, the structure and catalytic mechanism of SAHH exclude a role for Cu2+. In the present work, we studied the mechanism of inhibition of SAHH activity by Cu2+. The experimental results showed that Cu2+ inhibited SAHH activity in a noncompetitive manner. Binding of Cu2+ to SAHH resulted in the release of NAD+ cofactors, explaining the loss of the enzymatic activity of SAHH. Further investigation by an ESR probe and computational simulation suggested that Cu2+ could bind at the central channel and interrupt the subunit interactions of SAHH, resulting in a large decrease in affinity to the NAD+ cofactor. This effect of Cu2+ resembled that of enzyme mutations at the C-terminal domain or Asp244 [Komoto, J., Huang, Y., Gomi, T., Ogawa, H., Takata, Y., Fujioka, M., and Takusagawa, F. (2000) Effects of site-directed mutagenesis on structure and function of recombinant rat liver S-adenosylhomocysteine hydrolase. Crystal structure of D244E mutant enzyme, J. Biol. Chem. 275, 32147-32156]. The mechanism of action of Cu2+ on SAHH suggested a possible regulative role for Cu2+ on the intracellular activity of SAHH. This could be helpful in understanding the biological effects of copper compounds and suggest a potential coupling mechanism between biomethylation and the redox states of cells.

The Proteome of Copper, Iron, Zinc, and Manganese Micronutrient Deficiency in Chlamydomonas reinhardtii

“…At the same time, a third member of the pathway, serine hydroxymethyltransferase isoform 1, was increased 3-fold (supplemental Table S1). These results are interesting because the accumulation of another enzyme in the pathway, S-adenosylhomocysteine hydrolase, had been previously shown to be copper dependent, and copper is a non-competitive inhibitor of the enzyme in mouse liver (58,59). Although S-adenosylhomocysteine hydrolase was detected in our proteomics study, we did not observe a change in its abundance, which contrasts with results from the mouse model.…”

Acid sphingomyelinase-ceramide system in steatohepatitis: A novel target regulating multiple pathways

“…As mentioned above, Cu 2+ activates ASMase to cause erythrocyte and hepatocellular apoptosis that were prevented by ASMase inhibition with desipramine [108]. Further, Cu 2+ binds noncompetitively to SAHH resulting in its inhibition by releasing NAD + [142] and altered methionine metabolism has been described in Long-Evans Cinnamon rats, a model of Wilson's disease [143]. However, it remains to be established whether altered DNA methylation in this model contributes to ASMase activation and if ASMase inhibition by desipramine modulates methionine metabolism.…”

Wilson disease: At the crossroads between genetics and epigenetics—A review of the evidence

“…106 Methionine and ATP produce SAM via methionine adenosyltransferase (MAT).SAM is then converted to S-adenosylhomocysteine (SAH) through the bi-directional enzyme S-adenosylhomocysteine hydrolase (AHCY).ACHY is a key enzyme that regulates the amount of SAM that is available for methylation reactions. Copper inhibits ACHY, 107 leading to the accumulation of SAH, a reduction in SAM, the inhibition of MAT, and ultimately impaired methylation. 104 …”