Copper ions inhibit S-adenosylhomocysteine hydrolase by causing dissociation of NAD+ cofactor.
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.
Li
Mengyao
M
Department of Chemical Biology and State Key Laboratories of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing 100083, People's Republic of China.
Li
Yanjie
Y
Chen
Jiejin
J
Wei
Wei
W
Pan
Xiaowei
X
Liu
Jing
J
Liu
Qingyu
Q
Leu
Wei
W
Zhang
Liangren
L
Yang
Xiaoda
X
Lu
Jingfen
J
Wang
Kui
K
D043383:Adenosylhomocysteinase / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D001051:Apoenzymes / Q000737:chemistry / Q000378:metabolism; D003300:Copper / Q000494:pharmacology*; D015195:Drug Design; D005260:Female; D006801:Humans; D007700:Kinetics; D008872:Microwaves; D009243:NAD / Q000378:metabolism*; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy; D011485:Protein Binding; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry
D001051:Apoenzymes; D011994:Recombinant Proteins; D009243:NAD; D003300:Copper; D043383:Adenosylhomocysteinase